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From cf9b74986d5411ad5b976cbade1e4a070bdbd397 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 24 Sep 2021 21:49:45 +0800
Subject: [PATCH 01/42] onscreen/native: Keep the onscreen alive longer than
 `MetaDrmBufferGbm`

Because `MetaDrmBufferGbm` uses `gbm_surface` in its destructor and
`gbm_surface` can't be refcounted directly. So we reference its owner
(the onscreen) instead.

This avoids a crash that might otherwise occur when hotplugging monitors as
the old onscreen might get disposed before the new onscreen has presented
a replacement frame on the same `MetaKmsCrtc`.

We could instead wrap and refcount all users of `gbm_surface`, but that
would be a lot more work for no additional benefit right now.
---
 src/backends/native/meta-onscreen-native.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index a3ba447112b..149a25143dd 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -596,6 +596,16 @@ import_shared_framebuffer (CoglOnscreen                        *onscreen,
   return imported_buffer;
 }
 
+static void
+reference_owning_gbm_surface (CoglOnscreen     *onscreen,
+                              MetaDrmBufferGbm *buffer_gbm)
+{
+  g_object_set_data_full (G_OBJECT (buffer_gbm),
+                          "gbm_surface owner",
+                          g_object_ref (onscreen),
+                          (GDestroyNotify) g_object_unref);
+}
+
 static MetaDrmBuffer *
 copy_shared_framebuffer_gpu (CoglOnscreen                        *onscreen,
                              MetaOnscreenNativeSecondaryGpuState *secondary_gpu_state,
@@ -681,6 +691,8 @@ copy_shared_framebuffer_gpu (CoglOnscreen                        *onscreen,
       return NULL;
     }
 
+  reference_owning_gbm_surface (onscreen, buffer_gbm);
+
   g_object_set_qdata_full (G_OBJECT (buffer_gbm),
                            blit_source_quark,
                            g_object_ref (primary_gpu_fb),
@@ -1113,6 +1125,7 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
           return;
         }
 
+      reference_owning_gbm_surface (onscreen, buffer_gbm);
       primary_gpu_fb = META_DRM_BUFFER (g_steal_pointer (&buffer_gbm));
       break;
     case META_RENDERER_NATIVE_MODE_SURFACELESS:
-- 
GitLab

From ac3fdba59b9b58fbd9d25437854e9a3e8fdaa796 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Mon, 16 Aug 2021 17:06:43 +0800
Subject: [PATCH 02/42] kms/update: Hold a reference to the buffer used in a
 plane assignment

---
 src/backends/native/meta-kms-update.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/backends/native/meta-kms-update.c b/src/backends/native/meta-kms-update.c
index 7658db0ca61..5ca7056b863 100644
--- a/src/backends/native/meta-kms-update.c
+++ b/src/backends/native/meta-kms-update.c
@@ -192,6 +192,7 @@ static void
 meta_kms_plane_assignment_free (MetaKmsPlaneAssignment *plane_assignment)
 {
   g_clear_pointer (&plane_assignment->fb_damage, meta_kms_fb_damage_free);
+  g_clear_object (&plane_assignment->buffer);
   g_free (plane_assignment);
 }
 
@@ -301,7 +302,7 @@ meta_kms_update_assign_plane (MetaKmsUpdate          *update,
     .update = update,
     .crtc = crtc,
     .plane = plane,
-    .buffer = buffer,
+    .buffer = g_object_ref (buffer),
     .src_rect = src_rect,
     .dst_rect = dst_rect,
     .flags = flags,
-- 
GitLab

From ccf25689aec9ae3c4416080ebda587cbf0f92f0b Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Mon, 16 Aug 2021 18:04:10 +0800
Subject: [PATCH 03/42] native: Introduce MetaSwapChain to hold plane buffer
 references

---
 src/backends/native/meta-swap-chain.c | 149 ++++++++++++++++++++++++++
 src/backends/native/meta-swap-chain.h |  48 +++++++++
 src/meson.build                       |   2 +
 3 files changed, 199 insertions(+)
 create mode 100644 src/backends/native/meta-swap-chain.c
 create mode 100644 src/backends/native/meta-swap-chain.h

diff --git a/src/backends/native/meta-swap-chain.c b/src/backends/native/meta-swap-chain.c
new file mode 100644
index 00000000000..c3bed569d87
--- /dev/null
+++ b/src/backends/native/meta-swap-chain.c
@@ -0,0 +1,149 @@
+/*
+ * Copyright (C) 2022 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ *
+ * Author: Daniel van Vugt <daniel.van.vugt@canonical.com>
+ */
+
+#include "backends/native/meta-swap-chain.h"
+
+typedef struct
+{
+  GObject *front, *back;
+  gboolean back_is_set;
+} PlaneState;
+
+typedef struct _MetaSwapChainPrivate MetaSwapChainPrivate;
+struct _MetaSwapChainPrivate
+{
+  GHashTable *plane_states;
+};
+
+G_DEFINE_TYPE_WITH_PRIVATE (MetaSwapChain, meta_swap_chain, G_TYPE_OBJECT)
+
+MetaSwapChain *
+meta_swap_chain_new (void)
+{
+  return g_object_new (META_TYPE_SWAP_CHAIN, NULL);
+}
+
+void
+meta_swap_chain_push_buffer (MetaSwapChain *swap_chain,
+                             unsigned int   plane_id,
+                             GObject       *buffer)
+{
+  MetaSwapChainPrivate *priv =
+    meta_swap_chain_get_instance_private (swap_chain);
+  gpointer key = GUINT_TO_POINTER (plane_id);
+  PlaneState *plane_state;
+
+  plane_state = g_hash_table_lookup (priv->plane_states, key);
+  if (plane_state == NULL)
+    {
+      plane_state = g_new0 (PlaneState, 1);
+      g_hash_table_insert (priv->plane_states, key, plane_state);
+    }
+
+  plane_state->back_is_set = TRUE;  /* note buffer may be NULL */
+  g_set_object (&plane_state->back, buffer);
+}
+
+static void
+swap_plane_buffers (gpointer key,
+                    gpointer value,
+                    gpointer user_data)
+{
+  PlaneState *plane_state = value;
+
+  if (plane_state->back_is_set)
+    {
+      g_set_object (&plane_state->front, plane_state->back);
+      g_clear_object (&plane_state->back);
+      plane_state->back_is_set = FALSE;
+    }
+}
+
+void
+meta_swap_chain_swap_buffers (MetaSwapChain *swap_chain)
+{
+  MetaSwapChainPrivate *priv =
+    meta_swap_chain_get_instance_private (swap_chain);
+
+  g_hash_table_foreach (priv->plane_states, swap_plane_buffers, NULL);
+}
+
+void
+meta_swap_chain_release_buffers (MetaSwapChain *swap_chain)
+{
+  MetaSwapChainPrivate *priv =
+    meta_swap_chain_get_instance_private (swap_chain);
+
+  g_hash_table_remove_all (priv->plane_states);
+}
+
+static void
+meta_swap_chain_dispose (GObject *object)
+{
+  MetaSwapChain *swap_chain = META_SWAP_CHAIN (object);
+
+  meta_swap_chain_release_buffers (swap_chain);
+
+  G_OBJECT_CLASS (meta_swap_chain_parent_class)->dispose (object);
+}
+
+static void
+meta_swap_chain_finalize (GObject *object)
+{
+  MetaSwapChain *swap_chain = META_SWAP_CHAIN (object);
+  MetaSwapChainPrivate *priv =
+    meta_swap_chain_get_instance_private (swap_chain);
+
+  g_hash_table_unref (priv->plane_states);
+
+  G_OBJECT_CLASS (meta_swap_chain_parent_class)->finalize (object);
+}
+
+static void
+destroy_plane_state (gpointer data)
+{
+  PlaneState *plane_state = data;
+
+  g_clear_object (&plane_state->front);
+  g_clear_object (&plane_state->back);
+  g_free (plane_state);
+}
+
+static void
+meta_swap_chain_init (MetaSwapChain *swap_chain)
+{
+  MetaSwapChainPrivate *priv =
+    meta_swap_chain_get_instance_private (swap_chain);
+
+  priv->plane_states = g_hash_table_new_full (NULL,
+                                              NULL,
+                                              NULL,
+                                              destroy_plane_state);
+}
+
+static void
+meta_swap_chain_class_init (MetaSwapChainClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->dispose = meta_swap_chain_dispose;
+  object_class->finalize = meta_swap_chain_finalize;
+}
diff --git a/src/backends/native/meta-swap-chain.h b/src/backends/native/meta-swap-chain.h
new file mode 100644
index 00000000000..bad772b8929
--- /dev/null
+++ b/src/backends/native/meta-swap-chain.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2022 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ *
+ * Author: Daniel van Vugt <daniel.van.vugt@canonical.com>
+ */
+
+#ifndef META_SWAP_CHAIN_H
+#define META_SWAP_CHAIN_H
+
+#include <glib-object.h>
+
+#define META_TYPE_SWAP_CHAIN (meta_swap_chain_get_type ())
+G_DECLARE_DERIVABLE_TYPE (MetaSwapChain,
+                          meta_swap_chain,
+                          META, SWAP_CHAIN,
+                          GObject)
+
+struct _MetaSwapChainClass
+{
+  GObjectClass parent_class;
+};
+
+MetaSwapChain * meta_swap_chain_new (void);
+
+void meta_swap_chain_push_buffer (MetaSwapChain *swap_chain,
+                                  unsigned int   plane_id,
+                                  GObject       *buffer);
+
+void meta_swap_chain_swap_buffers (MetaSwapChain *swap_chain);
+
+void meta_swap_chain_release_buffers (MetaSwapChain *swap_chain);
+
+#endif /* META_SWAP_CHAIN_H */
diff --git a/src/meson.build b/src/meson.build
index f4efdee702e..5472b5122a2 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -846,6 +846,8 @@ if have_native_backend
     'backends/native/meta-seat-native.h',
     'backends/native/meta-stage-native.c',
     'backends/native/meta-stage-native.h',
+    'backends/native/meta-swap-chain.c',
+    'backends/native/meta-swap-chain.h',
     'backends/native/meta-thread-impl.c',
     'backends/native/meta-thread-impl.h',
     'backends/native/meta-thread-private.h',
-- 
GitLab

From 9dd01e2edaae1b23ee45f92ee9f61feaa309e3a9 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Wed, 18 Jan 2023 18:42:01 +0800
Subject: [PATCH 04/42] kms/crtc: Add a local swap chain

---
 src/backends/native/meta-kms-crtc.c | 21 +++++++++++++++++++++
 src/backends/native/meta-kms-crtc.h |  3 +++
 2 files changed, 24 insertions(+)

diff --git a/src/backends/native/meta-kms-crtc.c b/src/backends/native/meta-kms-crtc.c
index ad796e3c98e..c06eb62fafb 100644
--- a/src/backends/native/meta-kms-crtc.c
+++ b/src/backends/native/meta-kms-crtc.c
@@ -50,6 +50,8 @@ struct _MetaKmsCrtc
   MetaKmsCrtcState current_state;
 
   MetaKmsCrtcPropTable prop_table;
+
+  MetaSwapChain *swap_chain;
 };
 
 G_DEFINE_TYPE (MetaKmsCrtc, meta_kms_crtc, G_TYPE_OBJECT)
@@ -101,6 +103,12 @@ meta_kms_crtc_get_prop_drm_value (MetaKmsCrtc     *crtc,
   return meta_kms_prop_convert_value (prop, value);
 }
 
+MetaSwapChain *
+meta_kms_crtc_get_swap_chain (MetaKmsCrtc *crtc)
+{
+  return crtc->swap_chain;
+}
+
 gboolean
 meta_kms_crtc_is_active (MetaKmsCrtc *crtc)
 {
@@ -467,12 +475,23 @@ meta_kms_crtc_new (MetaKmsImplDevice  *impl_device,
   return crtc;
 }
 
+static void
+meta_kms_crtc_dispose (GObject *object)
+{
+  MetaKmsCrtc *crtc = META_KMS_CRTC (object);
+
+  meta_swap_chain_release_buffers (crtc->swap_chain);
+
+  G_OBJECT_CLASS (meta_kms_crtc_parent_class)->dispose (object);
+}
+
 static void
 meta_kms_crtc_finalize (GObject *object)
 {
   MetaKmsCrtc *crtc = META_KMS_CRTC (object);
 
   g_clear_pointer (&crtc->current_state.gamma.value, meta_gamma_lut_free);
+  g_clear_object (&crtc->swap_chain);
 
   G_OBJECT_CLASS (meta_kms_crtc_parent_class)->finalize (object);
 }
@@ -482,6 +501,7 @@ meta_kms_crtc_init (MetaKmsCrtc *crtc)
 {
   crtc->current_state.gamma.size = 0;
   crtc->current_state.gamma.value = NULL;
+  crtc->swap_chain = meta_swap_chain_new ();
 }
 
 static void
@@ -489,6 +509,7 @@ meta_kms_crtc_class_init (MetaKmsCrtcClass *klass)
 {
   GObjectClass *object_class = G_OBJECT_CLASS (klass);
 
+  object_class->dispose = meta_kms_crtc_dispose;
   object_class->finalize = meta_kms_crtc_finalize;
 }
 
diff --git a/src/backends/native/meta-kms-crtc.h b/src/backends/native/meta-kms-crtc.h
index b7c8dd426c8..1a0ae08fcb1 100644
--- a/src/backends/native/meta-kms-crtc.h
+++ b/src/backends/native/meta-kms-crtc.h
@@ -24,6 +24,7 @@
 #include <xf86drmMode.h>
 
 #include "backends/native/meta-kms-types.h"
+#include "backends/native/meta-swap-chain.h"
 #include "backends/meta-backend-types.h"
 #include "core/util-private.h"
 #include "meta/boxes.h"
@@ -62,3 +63,5 @@ int meta_kms_crtc_get_idx (MetaKmsCrtc *crtc);
 
 META_EXPORT_TEST
 gboolean meta_kms_crtc_is_active (MetaKmsCrtc *crtc);
+
+MetaSwapChain * meta_kms_crtc_get_swap_chain (MetaKmsCrtc *crtc);
-- 
GitLab

From 47114814eb0a4b4b2e3c3ba3f88acac09388ffc8 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 17 Aug 2021 16:35:18 +0800
Subject: [PATCH 05/42] onscreen/native: Pump the CRTC's buffer reference queue
 on scanout

Precise timing of this call is not important. We only need to notify
that the *previous* scanout is definitely no longer happening. So any
old buffers no longer used in the latest scanout can be released.
---
 src/backends/native/meta-onscreen-native.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 149a25143dd..255d6d11979 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -229,6 +229,7 @@ notify_view_crtc_presented (MetaRendererView *view,
 
   meta_onscreen_native_notify_frame_complete (onscreen);
   meta_onscreen_native_swap_drm_fb (onscreen);
+  meta_swap_chain_swap_buffers (meta_kms_crtc_get_swap_chain (kms_crtc));
 }
 
 static void
-- 
GitLab

From 1c2c159f105e36d9ec70d8d14d047f2cbb9dd419 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Wed, 9 Feb 2022 16:44:09 +0800
Subject: [PATCH 06/42] kms/impl-device: Release buffers from MetaKmsCrtc in
 prepare_shutdown

This allows them to release their buffers cleanly while all the
associated resources to do the release still exist. Otherwise we
might crash later in meta_drm_buffer_finalize.
---
 src/backends/native/meta-kms-impl-device.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/backends/native/meta-kms-impl-device.c b/src/backends/native/meta-kms-impl-device.c
index d4ed82a6d87..2f9a22a923f 100644
--- a/src/backends/native/meta-kms-impl-device.c
+++ b/src/backends/native/meta-kms-impl-device.c
@@ -1849,6 +1849,16 @@ meta_kms_impl_device_init_mode_setting (MetaKmsImplDevice  *impl_device,
   return TRUE;
 }
 
+static void
+release_buffers (gpointer data,
+                 gpointer user_data)
+{
+  MetaKmsCrtc *crtc = data;
+  MetaSwapChain *swap_chain = meta_kms_crtc_get_swap_chain (crtc);
+
+  meta_swap_chain_release_buffers (swap_chain);
+}
+
 void
 meta_kms_impl_device_prepare_shutdown (MetaKmsImplDevice *impl_device)
 {
@@ -1856,6 +1866,8 @@ meta_kms_impl_device_prepare_shutdown (MetaKmsImplDevice *impl_device)
     meta_kms_impl_device_get_instance_private (impl_device);
   MetaKmsImplDeviceClass *klass = META_KMS_IMPL_DEVICE_GET_CLASS (impl_device);
 
+  g_list_foreach (priv->crtcs, release_buffers, NULL);
+
   if (klass->prepare_shutdown)
     klass->prepare_shutdown (impl_device);
 
-- 
GitLab

From d647891c353fa2d3fea1472ebcf88e6edf345388 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 7 Dec 2021 18:31:16 +0800
Subject: [PATCH 07/42] kms/impl-device/simple: Pump the CRTC's buffer
 reference queue on scanout

In this case "on scanout" means when `drmModeSetCrtc` succeeds. This is
the only case where there won't be a `meta_kms_page_flip_data_flipped` to
do it for us.
---
 src/backends/native/meta-kms-impl-device-simple.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/backends/native/meta-kms-impl-device-simple.c b/src/backends/native/meta-kms-impl-device-simple.c
index 291e9e7bfa6..be012e0590c 100644
--- a/src/backends/native/meta-kms-impl-device-simple.c
+++ b/src/backends/native/meta-kms-impl-device-simple.c
@@ -487,6 +487,8 @@ process_mode_set (MetaKmsImplDevice  *impl_device,
       return FALSE;
     }
 
+  meta_swap_chain_swap_buffers (meta_kms_crtc_get_swap_chain (crtc));
+
   if (drm_mode)
     {
       g_hash_table_replace (impl_device_simple->cached_mode_sets,
@@ -879,6 +881,8 @@ mode_set_fallback (MetaKmsImplDeviceSimple  *impl_device_simple,
       return FALSE;
     }
 
+  meta_swap_chain_swap_buffers (meta_kms_crtc_get_swap_chain (crtc));
+
   if (!impl_device_simple->mode_set_fallback_feedback_source)
     {
       MetaKmsImpl *impl = meta_kms_impl_device_get_impl (impl_device);
-- 
GitLab

From 49c2a69a36b7f1ffe05b0dcbfba043a720580745 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 17 Aug 2021 17:40:57 +0800
Subject: [PATCH 08/42] kms/impl-device/simple: Keep a reference to buffers
 assigned to planes

The MetaKmsCrtc will hold these references during future scanouts until
such time as a new buffer is assigned to the plane AND another scanout
has occurred after that.
---
 src/backends/native/meta-kms-impl-device-simple.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/backends/native/meta-kms-impl-device-simple.c b/src/backends/native/meta-kms-impl-device-simple.c
index be012e0590c..2679aafc7f3 100644
--- a/src/backends/native/meta-kms-impl-device-simple.c
+++ b/src/backends/native/meta-kms-impl-device-simple.c
@@ -1305,7 +1305,7 @@ process_plane_assignment (MetaKmsImplDevice       *impl_device,
     {
     case META_KMS_PLANE_TYPE_PRIMARY:
       /* Handled as part of the mode-set and page flip. */
-      return TRUE;
+      goto assigned;
     case META_KMS_PLANE_TYPE_CURSOR:
       if (!process_cursor_plane_assignment (impl_device, update,
                                             plane_assignment,
@@ -1319,7 +1319,7 @@ process_plane_assignment (MetaKmsImplDevice       *impl_device,
         }
       else
         {
-          return TRUE;
+          goto assigned;
         }
     case META_KMS_PLANE_TYPE_OVERLAY:
       error = g_error_new_literal (G_IO_ERROR, G_IO_ERROR_FAILED,
@@ -1332,6 +1332,12 @@ process_plane_assignment (MetaKmsImplDevice       *impl_device,
     }
 
   g_assert_not_reached ();
+
+assigned:
+  meta_swap_chain_push_buffer (meta_kms_crtc_get_swap_chain (plane_assignment->crtc),
+                               meta_kms_plane_get_id (plane),
+                               G_OBJECT (plane_assignment->buffer));
+  return TRUE;
 }
 
 static gboolean
-- 
GitLab

From aaa481391f6f1a0216f3eea442a5befe6a164d4a Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 7 Dec 2021 17:54:15 +0800
Subject: [PATCH 09/42] kms/impl-device/simple: Keep a reference to buffers
 needed in retries

---
 .../native/meta-kms-impl-device-simple.c      | 24 ++++++++++++-------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/backends/native/meta-kms-impl-device-simple.c b/src/backends/native/meta-kms-impl-device-simple.c
index 2679aafc7f3..da35ba44129 100644
--- a/src/backends/native/meta-kms-impl-device-simple.c
+++ b/src/backends/native/meta-kms-impl-device-simple.c
@@ -558,7 +558,7 @@ is_timestamp_earlier_than (uint64_t ts1,
 typedef struct _RetryPageFlipData
 {
   MetaKmsCrtc *crtc;
-  uint32_t fb_id;
+  MetaDrmBuffer *fb;
   MetaKmsPageFlipData *page_flip_data;
   float refresh_rate;
   uint64_t retry_time_us;
@@ -571,6 +571,7 @@ retry_page_flip_data_free (RetryPageFlipData *retry_page_flip_data)
   g_assert (!retry_page_flip_data->page_flip_data);
   g_clear_pointer (&retry_page_flip_data->custom_page_flip,
                    meta_kms_custom_page_flip_free);
+  g_clear_object (&retry_page_flip_data->fb);
   g_free (retry_page_flip_data);
 }
 
@@ -638,16 +639,21 @@ retry_page_flips (gpointer user_data)
         }
       else
         {
+          uint32_t fb_id =
+            retry_page_flip_data->fb ?
+            meta_drm_buffer_get_fb_id (retry_page_flip_data->fb) :
+            0;
+
           meta_topic (META_DEBUG_KMS,
                       "[simple] Retrying page flip on CRTC %u (%s) with %u",
                       meta_kms_crtc_get_id (crtc),
                       meta_kms_impl_device_get_path (impl_device),
-                      retry_page_flip_data->fb_id);
+                      fb_id);
 
           fd = meta_kms_impl_device_get_fd (impl_device);
           ret = drmModePageFlip (fd,
                                  meta_kms_crtc_get_id (crtc),
-                                 retry_page_flip_data->fb_id,
+                                 fb_id,
                                  DRM_MODE_PAGE_FLIP_EVENT,
                                  retry_page_flip_data->page_flip_data);
         }
@@ -734,7 +740,7 @@ retry_page_flips (gpointer user_data)
 static void
 schedule_retry_page_flip (MetaKmsImplDeviceSimple *impl_device_simple,
                           MetaKmsCrtc             *crtc,
-                          uint32_t                 fb_id,
+                          MetaDrmBuffer           *fb,
                           float                    refresh_rate,
                           MetaKmsPageFlipData     *page_flip_data,
                           MetaKmsCustomPageFlip   *custom_page_flip)
@@ -749,7 +755,7 @@ schedule_retry_page_flip (MetaKmsImplDeviceSimple *impl_device_simple,
   retry_page_flip_data = g_new0 (RetryPageFlipData, 1);
   *retry_page_flip_data = (RetryPageFlipData) {
     .crtc = crtc,
-    .fb_id = fb_id,
+    .fb = fb ? g_object_ref (fb) : NULL,
     .page_flip_data = page_flip_data,
     .refresh_rate = refresh_rate,
     .retry_time_us = retry_time_us,
@@ -1009,20 +1015,20 @@ dispatch_page_flip (MetaKmsImplDevice    *impl_device,
       cached_mode_set = get_cached_mode_set (impl_device_simple, crtc);
       if (cached_mode_set)
         {
-          uint32_t fb_id;
+          MetaDrmBuffer *fb;
           drmModeModeInfo *drm_mode;
           float refresh_rate;
 
           if (plane_assignment)
-            fb_id = meta_drm_buffer_get_fb_id (plane_assignment->buffer);
+            fb = plane_assignment->buffer;
           else
-            fb_id = 0;
+            fb = NULL;
           drm_mode = cached_mode_set->drm_mode;
           refresh_rate = meta_calculate_drm_mode_refresh_rate (drm_mode);
           meta_kms_impl_device_hold_fd (impl_device);
           schedule_retry_page_flip (impl_device_simple,
                                     crtc,
-                                    fb_id,
+                                    fb,
                                     refresh_rate,
                                     page_flip_data,
                                     g_steal_pointer (&custom_page_flip));
-- 
GitLab

From 7c4e737fefa395d95b86b667c11424260e694ca6 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 17 Aug 2021 16:36:25 +0800
Subject: [PATCH 10/42] kms/impl-device/atomic: Keep a reference to buffers
 assigned to planes

The MetaKmsCrtc will hold these references during future scanouts until
such time as a new buffer is assigned to the plane AND another scanout
has occurred after that.
---
 src/backends/native/meta-kms-impl-device-atomic.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/backends/native/meta-kms-impl-device-atomic.c b/src/backends/native/meta-kms-impl-device-atomic.c
index 5e58bb5499b..939eb7c7b1d 100644
--- a/src/backends/native/meta-kms-impl-device-atomic.c
+++ b/src/backends/native/meta-kms-impl-device-atomic.c
@@ -507,6 +507,7 @@ process_plane_assignment (MetaKmsImplDevice  *impl_device,
 {
   MetaKmsPlaneAssignment *plane_assignment = update_entry;
   MetaKmsPlane *plane = plane_assignment->plane;
+  MetaKmsUpdateFlag flags = (MetaKmsUpdateFlag) user_data;
   MetaDrmBuffer *buffer;
   MetaKmsFbDamage *fb_damage;
   uint32_t prop_id;
@@ -659,6 +660,12 @@ process_plane_assignment (MetaKmsImplDevice  *impl_device,
                                error))
         return FALSE;
     }
+
+  if (!(flags & META_KMS_UPDATE_FLAG_TEST_ONLY))
+    meta_swap_chain_push_buffer (meta_kms_crtc_get_swap_chain (plane_assignment->crtc),
+                                 meta_kms_plane_get_id (plane),
+                                 G_OBJECT (buffer));
+
   return TRUE;
 }
 
@@ -1003,7 +1010,7 @@ meta_kms_impl_device_atomic_process_update (MetaKmsImplDevice *impl_device,
                         req,
                         blob_ids,
                         meta_kms_update_get_plane_assignments (update),
-                        NULL,
+                        GUINT_TO_POINTER (flags),
                         process_plane_assignment,
                         &error))
     goto err;
-- 
GitLab

From 54baf587834bc2b0150167d0b5ea1f3808c1940e Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Wed, 18 Aug 2021 15:04:27 +0800
Subject: [PATCH 11/42] onscreen/native: Stop holding the current onscreen
 buffer

The scanout lifetime of the buffer is now automatically managed via
meta_crtc_kms_assign_primary_plane. Se we don't need `current_fb` at
all, and `next_fb` can be unreferenced as soon as we've passed it to
meta_crtc_kms_assign_primary_plane.
---
 src/backends/native/meta-onscreen-native.c | 43 ++--------------------
 1 file changed, 4 insertions(+), 39 deletions(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 255d6d11979..6f7aa69d766 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -93,7 +93,6 @@ struct _MetaOnscreenNative
 
   struct {
     struct gbm_surface *surface;
-    MetaDrmBuffer *current_fb;
     MetaDrmBuffer *next_fb;
   } gbm;
 
@@ -128,36 +127,6 @@ init_secondary_gpu_state (MetaRendererNative  *renderer_native,
                           CoglOnscreen        *onscreen,
                           GError             **error);
 
-static void
-free_current_bo (CoglOnscreen *onscreen)
-{
-  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
-
-  g_clear_object (&onscreen_native->gbm.current_fb);
-}
-
-static void
-meta_onscreen_native_swap_drm_fb (CoglOnscreen *onscreen)
-{
-  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
-
-  if (!onscreen_native->gbm.next_fb)
-    return;
-
-  free_current_bo (onscreen);
-
-  g_set_object (&onscreen_native->gbm.current_fb, onscreen_native->gbm.next_fb);
-  g_clear_object (&onscreen_native->gbm.next_fb);
-}
-
-static void
-meta_onscreen_native_clear_next_fb (CoglOnscreen *onscreen)
-{
-  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
-
-  g_clear_object (&onscreen_native->gbm.next_fb);
-}
-
 static void
 maybe_update_frame_info (MetaCrtc         *crtc,
                          CoglFrameInfo    *frame_info,
@@ -228,7 +197,6 @@ notify_view_crtc_presented (MetaRendererView *view,
   maybe_update_frame_info (crtc, frame_info, time_us, flags, sequence);
 
   meta_onscreen_native_notify_frame_complete (onscreen);
-  meta_onscreen_native_swap_drm_fb (onscreen);
   meta_swap_chain_swap_buffers (meta_kms_crtc_get_swap_chain (kms_crtc));
 }
 
@@ -337,7 +305,6 @@ page_flip_feedback_discarded (MetaKmsCrtc  *kms_crtc,
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
 
   meta_onscreen_native_notify_frame_complete (onscreen);
-  meta_onscreen_native_clear_next_fb (onscreen);
 }
 
 static const MetaKmsPageFlipListenerVtable page_flip_listener_vtable = {
@@ -402,8 +369,9 @@ void
 meta_onscreen_native_dummy_power_save_page_flip (CoglOnscreen *onscreen)
 {
   CoglFrameInfo *frame_info;
+  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
 
-  meta_onscreen_native_swap_drm_fb (onscreen);
+  g_clear_object (&onscreen_native->gbm.next_fb);
 
   frame_info = cogl_onscreen_peek_tail_frame_info (onscreen);
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
@@ -426,7 +394,7 @@ meta_onscreen_native_flip_crtc (CoglOnscreen                *onscreen,
   MetaKmsCrtc *kms_crtc = meta_crtc_kms_get_kms_crtc (crtc_kms);
   MetaRendererNativeGpuData *renderer_gpu_data;
   MetaGpuKms *gpu_kms;
-  MetaDrmBuffer *buffer;
+  g_autoptr (MetaDrmBuffer) buffer = NULL;
   MetaKmsPlaneAssignment *plane_assignment;
 
   COGL_TRACE_BEGIN_SCOPED (MetaOnscreenNativeFlipCrtcs,
@@ -441,7 +409,7 @@ meta_onscreen_native_flip_crtc (CoglOnscreen                *onscreen,
   switch (renderer_gpu_data->mode)
     {
     case META_RENDERER_NATIVE_MODE_GBM:
-      buffer = onscreen_native->gbm.next_fb;
+      buffer = g_steal_pointer (&onscreen_native->gbm.next_fb);
 
       plane_assignment = meta_crtc_kms_assign_primary_plane (crtc_kms,
                                                              buffer,
@@ -1045,7 +1013,6 @@ swap_buffer_result_feedback (const MetaKmsFeedback *kms_feedback,
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
 
   meta_onscreen_native_notify_frame_complete (onscreen);
-  meta_onscreen_native_clear_next_fb (onscreen);
 }
 
 static const MetaKmsResultListenerVtable swap_buffer_result_listener_vtable = {
@@ -1333,7 +1300,6 @@ scanout_result_feedback (const MetaKmsFeedback *kms_feedback,
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
 
   meta_onscreen_native_notify_frame_complete (onscreen);
-  meta_onscreen_native_clear_next_fb (onscreen);
 }
 
 static const MetaKmsResultListenerVtable scanout_result_listener_vtable = {
@@ -2429,7 +2395,6 @@ meta_onscreen_native_dispose (GObject *object)
     {
     case META_RENDERER_NATIVE_MODE_GBM:
       g_clear_object (&onscreen_native->gbm.next_fb);
-      free_current_bo (onscreen);
       break;
     case META_RENDERER_NATIVE_MODE_SURFACELESS:
       g_assert_not_reached ();
-- 
GitLab

From 55b13fd9f623ef2663128a5157267bedb909220a Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 2 Mar 2023 18:01:26 +0800
Subject: [PATCH 12/42] FIXME: Temporary workaround for the scanout-failed
 signal

---
 src/backends/native/meta-onscreen-native.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 6f7aa69d766..89cb36267e2 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -94,6 +94,11 @@ struct _MetaOnscreenNative
   struct {
     struct gbm_surface *surface;
     MetaDrmBuffer *next_fb;
+
+    /* Temporary workaround for the scanout-failed signal wanting the buffer
+     * to live longer than it does, and then it doesn't use it anyway...
+     */
+    MetaDrmBuffer *direct_fb;
   } gbm;
 
 #ifdef HAVE_EGL_DEVICE
@@ -1277,6 +1282,7 @@ scanout_result_feedback (const MetaKmsFeedback *kms_feedback,
   CoglOnscreen *onscreen = COGL_ONSCREEN (onscreen_native);
   const GError *error;
   CoglFrameInfo *frame_info;
+  g_autoptr (MetaDrmBuffer) direct_fb = g_steal_pointer (&onscreen_native->gbm.direct_fb);
 
   error = meta_kms_feedback_get_error (kms_feedback);
   if (!error)
@@ -1290,8 +1296,7 @@ scanout_result_feedback (const MetaKmsFeedback *kms_feedback,
 
       g_warning ("Direct scanout page flip failed: %s", error->message);
 
-      cogl_scanout_notify_failed (COGL_SCANOUT (onscreen_native->gbm.next_fb),
-                                  onscreen);
+      cogl_scanout_notify_failed (COGL_SCANOUT (direct_fb), onscreen);
       clutter_stage_view_add_redraw_clip (view, NULL);
       clutter_stage_view_schedule_update_now (view);
     }
@@ -1365,6 +1370,8 @@ meta_onscreen_native_direct_scanout (CoglOnscreen   *onscreen,
   kms_device = meta_kms_crtc_get_device (kms_crtc);
   kms_update = meta_frame_native_ensure_kms_update (frame_native, kms_device);
 
+  g_set_object (&onscreen_native->gbm.direct_fb,
+                onscreen_native->gbm.next_fb);
   meta_kms_update_add_result_listener (kms_update,
                                        &scanout_result_listener_vtable,
                                        NULL,
@@ -2395,6 +2402,7 @@ meta_onscreen_native_dispose (GObject *object)
     {
     case META_RENDERER_NATIVE_MODE_GBM:
       g_clear_object (&onscreen_native->gbm.next_fb);
+      g_clear_object (&onscreen_native->gbm.direct_fb);
       break;
     case META_RENDERER_NATIVE_MODE_SURFACELESS:
       g_assert_not_reached ();
-- 
GitLab

From d60cac7b328c7b1cca406cd389bab993b1f337e6 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 17 Sep 2021 17:48:20 +0800
Subject: [PATCH 13/42] cogl/onscreen: Add function
 cogl_onscreen_count_pending_frames

---
 cogl/cogl/cogl-onscreen-private.h | 3 +++
 cogl/cogl/cogl-onscreen.c         | 8 ++++++++
 2 files changed, 11 insertions(+)

diff --git a/cogl/cogl/cogl-onscreen-private.h b/cogl/cogl/cogl-onscreen-private.h
index 9dbecfd0c99..681d91d2b08 100644
--- a/cogl/cogl/cogl-onscreen-private.h
+++ b/cogl/cogl/cogl-onscreen-private.h
@@ -95,3 +95,6 @@ cogl_onscreen_peek_tail_frame_info (CoglOnscreen *onscreen);
 
 COGL_EXPORT CoglFrameInfo *
 cogl_onscreen_pop_head_frame_info (CoglOnscreen *onscreen);
+
+COGL_EXPORT unsigned int
+cogl_onscreen_count_pending_frames (CoglOnscreen *onscreen);
diff --git a/cogl/cogl/cogl-onscreen.c b/cogl/cogl/cogl-onscreen.c
index 73425e49855..02c4474b2da 100644
--- a/cogl/cogl/cogl-onscreen.c
+++ b/cogl/cogl/cogl-onscreen.c
@@ -508,6 +508,14 @@ cogl_onscreen_pop_head_frame_info (CoglOnscreen *onscreen)
   return g_queue_pop_head (&priv->pending_frame_infos);
 }
 
+unsigned int
+cogl_onscreen_count_pending_frames (CoglOnscreen *onscreen)
+{
+  CoglOnscreenPrivate *priv = cogl_onscreen_get_instance_private (onscreen);
+
+  return g_queue_get_length (&priv->pending_frame_infos);
+}
+
 CoglFrameClosure *
 cogl_onscreen_add_frame_callback (CoglOnscreen *onscreen,
                                   CoglFrameCallback callback,
-- 
GitLab

From bac6f06b9b1248c468a6316ab4cad673b6e9a4b9 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Wed, 20 Apr 2022 18:33:43 +0800
Subject: [PATCH 14/42] kms: Keep a shutting_down flag

---
 src/backends/native/meta-kms.c | 9 +++++++++
 src/backends/native/meta-kms.h | 2 ++
 2 files changed, 11 insertions(+)

diff --git a/src/backends/native/meta-kms.c b/src/backends/native/meta-kms.c
index 31249adde89..00d1ed23e48 100644
--- a/src/backends/native/meta-kms.c
+++ b/src/backends/native/meta-kms.c
@@ -157,6 +157,8 @@ struct _MetaKms
   int kernel_thread_inhibit_count;
 
   MetaKmsCursorManager *cursor_manager;
+
+  gboolean shutting_down;
 };
 
 G_DEFINE_TYPE (MetaKms, meta_kms, META_TYPE_THREAD)
@@ -435,6 +437,7 @@ static void
 on_prepare_shutdown (MetaBackend *backend,
                      MetaKms     *kms)
 {
+  kms->shutting_down = TRUE;
   meta_kms_run_impl_task_sync (kms, prepare_shutdown_in_impl, NULL, NULL);
   meta_thread_flush_callbacks (META_THREAD (kms));
 
@@ -489,6 +492,12 @@ meta_kms_new (MetaBackend   *backend,
   return kms;
 }
 
+gboolean
+meta_kms_is_shutting_down (MetaKms *kms)
+{
+  return kms->shutting_down;
+}
+
 static void
 meta_kms_finalize (GObject *object)
 {
diff --git a/src/backends/native/meta-kms.h b/src/backends/native/meta-kms.h
index f40b6281b94..09450a68c95 100644
--- a/src/backends/native/meta-kms.h
+++ b/src/backends/native/meta-kms.h
@@ -62,6 +62,8 @@ MetaKmsDevice * meta_kms_create_device (MetaKms            *kms,
                                         MetaKmsDeviceFlag   flags,
                                         GError            **error);
 
+gboolean meta_kms_is_shutting_down (MetaKms *kms);
+
 MetaKms * meta_kms_new (MetaBackend   *backend,
                         MetaKmsFlags   flags,
                         GError       **error);
-- 
GitLab

From a6cc585a4678fd6a959492b5b07ab91bef889c54 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 26 Oct 2021 18:50:50 +0800
Subject: [PATCH 15/42] renderer/native: Avoid requeuing the same onscreen for
 a power save flip

This is a case that triple buffering will encounter. We don't want it
to queue the same onscreen multiple times because that would represent
multiple flips occurring simultaneously.

It's a linear search but the list length is typically only 1 or 2 so
no need for anything fancier yet.
---
 src/backends/native/meta-renderer-native.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index 6826fe92556..817e0d5a538 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -705,6 +705,9 @@ meta_renderer_native_queue_power_save_page_flip (MetaRendererNative *renderer_na
 {
   const unsigned int timeout_ms = 100;
 
+  if (g_list_find (renderer_native->power_save_page_flip_onscreens, onscreen))
+    return;
+
   if (!renderer_native->power_save_page_flip_source_id)
     {
       renderer_native->power_save_page_flip_source_id =
-- 
GitLab

From d64adaa5c0934edaab7d7e568003c0ed1be3fc3d Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Mon, 1 Nov 2021 19:35:34 +0800
Subject: [PATCH 16/42] renderer/native: Steal the power save flip list before
 iterating over it

Because a single iteration might also grow the list again.
---
 src/backends/native/meta-renderer-native.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index 817e0d5a538..a9c5e73f46e 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -688,12 +688,18 @@ static gboolean
 dummy_power_save_page_flip_cb (gpointer user_data)
 {
   MetaRendererNative *renderer_native = user_data;
+  GList *old_list =
+    g_steal_pointer (&renderer_native->power_save_page_flip_onscreens);
 
-  g_list_foreach (renderer_native->power_save_page_flip_onscreens,
+  g_list_foreach (old_list,
                   (GFunc) meta_onscreen_native_dummy_power_save_page_flip,
                   NULL);
-  g_clear_list (&renderer_native->power_save_page_flip_onscreens,
+  g_clear_list (&old_list,
                 g_object_unref);
+
+  if (renderer_native->power_save_page_flip_onscreens != NULL)
+    return G_SOURCE_CONTINUE;
+
   renderer_native->power_save_page_flip_source_id = 0;
 
   return G_SOURCE_REMOVE;
-- 
GitLab

From 9b07674182fe17d582e4e727329c5f17af3a2aff Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 10 Dec 2021 16:40:58 +0800
Subject: [PATCH 17/42] onscreen/native: Log swapbuffers and N-buffering when
 MUTTER_DEBUG=kms

---
 src/backends/native/meta-onscreen-native.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 89cb36267e2..54536fc2054 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -1062,6 +1062,19 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
   COGL_TRACE_BEGIN_SCOPED (MetaRendererNativeSwapBuffers,
                            "Onscreen (swap-buffers)");
 
+  if (meta_is_topic_enabled (META_DEBUG_KMS))
+    {
+      unsigned int frames_pending =
+        cogl_onscreen_count_pending_frames (onscreen);
+
+      meta_topic (META_DEBUG_KMS,
+                  "Swap buffers: %u frames pending (%s-buffering)",
+                  frames_pending,
+                  frames_pending == 1 ? "double" :
+                  frames_pending == 2 ? "triple" :
+                  "?");
+    }
+
   secondary_gpu_fb =
     update_secondary_gpu_state_pre_swap_buffers (onscreen,
                                                  rectangles,
-- 
GitLab

From 4295bc4998f1e8f195a049ddf0c5383081dad82e Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Wed, 28 Jul 2021 16:35:56 +0800
Subject: [PATCH 18/42] onscreen/native: Replace an assertion that double
 buffering is the maximum

Because it soon won't be the maximum. But we do want to verify that the
frame info queue is not empty, to avoid NULL dereferencing and catch logic
errors.
---
 src/backends/native/meta-onscreen-native.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 54536fc2054..466e2e060dc 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -167,7 +167,7 @@ meta_onscreen_native_notify_frame_complete (CoglOnscreen *onscreen)
 
   info = cogl_onscreen_pop_head_frame_info (onscreen);
 
-  g_assert (!cogl_onscreen_peek_head_frame_info (onscreen));
+  g_assert (info);
 
   _cogl_onscreen_notify_frame_sync (onscreen, info);
   _cogl_onscreen_notify_complete (onscreen, info);
-- 
GitLab

From fb60c3b105d2f95035f2b18acbc8e88c35b9e7a7 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 16 Sep 2021 16:26:25 +0800
Subject: [PATCH 19/42] onscreen/native: Deduplicate calls to
 clutter_frame_set_result

All paths out of `meta_onscreen_native_swap_buffers_with_damage` from
here onward would set the same `CLUTTER_FRAME_RESULT_PENDING_PRESENTED`
(or terminate with `g_assert_not_reached`).

Even failed posts set this result because they will do a
`meta_onscreen_native_notify_frame_complete` in
`page_flip_feedback_discarded`.
---
 src/backends/native/meta-onscreen-native.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 466e2e060dc..de9645e2434 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -1145,6 +1145,9 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
 #endif
     }
 
+  clutter_frame_set_result (frame,
+                            CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
+
   /*
    * If we changed EGL context, cogl will have the wrong idea about what is
    * current, making it fail to set it when it needs to. Avoid that by making
@@ -1181,8 +1184,6 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
     {
       meta_renderer_native_queue_power_save_page_flip (renderer_native,
                                                        onscreen);
-      clutter_frame_set_result (frame,
-                                CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
       return;
     }
 
@@ -1202,8 +1203,6 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
           kms_update = meta_frame_native_steal_kms_update (frame_native);
           meta_renderer_native_queue_mode_set_update (renderer_native,
                                                       kms_update);
-          clutter_frame_set_result (frame,
-                                    CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
           return;
         }
       else if (meta_renderer_native_has_pending_mode_set (renderer_native))
@@ -1217,8 +1216,6 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
 
           meta_frame_native_steal_kms_update (frame_native);
           meta_renderer_native_post_mode_set_updates (renderer_native);
-          clutter_frame_set_result (frame,
-                                    CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
           return;
         }
       break;
@@ -1234,8 +1231,6 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
                                                       kms_update);
 
           meta_renderer_native_post_mode_set_updates (renderer_native);
-          clutter_frame_set_result (frame,
-                                    CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
           return;
         }
       break;
@@ -1250,7 +1245,6 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
   kms_update = meta_frame_native_steal_kms_update (frame_native);
   meta_kms_device_post_update (kms_device, kms_update,
                                META_KMS_UPDATE_FLAG_NONE);
-  clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
 }
 
 gboolean
-- 
GitLab

From dc3d109f8d39ca5868a55177f45407dfcc92e8fd Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Wed, 28 Jul 2021 16:29:27 +0800
Subject: [PATCH 20/42] onscreen/native: Split swap_buffers_with_damage into
 two functions

1. The EGL part: meta_onscreen_native_swap_buffers_with_damage
2. The KMS part: post_latest_swap
---
 src/backends/native/meta-onscreen-native.c | 66 +++++++++++++++++-----
 1 file changed, 53 insertions(+), 13 deletions(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index de9645e2434..50395ea070c 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -120,6 +120,12 @@ struct _MetaOnscreenNative
   gulong privacy_screen_changed_handler_id;
   gulong color_space_changed_handler_id;
   gulong hdr_metadata_changed_handler_id;
+
+  struct {
+    int *rectangles;  /* 4 x n_rectangles */
+    int n_rectangles;
+    ClutterFrame *frame;
+  } next_post;
 };
 
 G_DEFINE_TYPE (MetaOnscreenNative, meta_onscreen_native,
@@ -127,6 +133,9 @@ G_DEFINE_TYPE (MetaOnscreenNative, meta_onscreen_native,
 
 static GQuark blit_source_quark = 0;
 
+static void
+post_latest_swap (CoglOnscreen *onscreen);
+
 static gboolean
 init_secondary_gpu_state (MetaRendererNative  *renderer_native,
                           CoglOnscreen        *onscreen,
@@ -1038,26 +1047,18 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
   CoglRendererEGL *cogl_renderer_egl = cogl_renderer->winsys;
   MetaRendererNativeGpuData *renderer_gpu_data = cogl_renderer_egl->platform;
   MetaRendererNative *renderer_native = renderer_gpu_data->renderer_native;
-  MetaRenderer *renderer = META_RENDERER (renderer_native);
-  MetaBackend *backend = meta_renderer_get_backend (renderer);
-  MetaMonitorManager *monitor_manager =
-    meta_backend_get_monitor_manager (backend);
   MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
   MetaGpuKms *render_gpu = onscreen_native->render_gpu;
   MetaDeviceFile *render_device_file;
   ClutterFrame *frame = user_data;
-  MetaFrameNative *frame_native = meta_frame_native_from_frame (frame);
-  MetaKmsUpdate *kms_update;
   CoglOnscreenClass *parent_class;
   gboolean egl_context_changed = FALSE;
-  MetaPowerSave power_save_mode;
   g_autoptr (GError) error = NULL;
   MetaDrmBufferFlags buffer_flags;
   MetaDrmBufferGbm *buffer_gbm;
   g_autoptr (MetaDrmBuffer) primary_gpu_fb = NULL;
   g_autoptr (MetaDrmBuffer) secondary_gpu_fb = NULL;
-  MetaKmsCrtc *kms_crtc;
-  MetaKmsDevice *kms_device;
+  size_t rectangles_size;
 
   COGL_TRACE_BEGIN_SCOPED (MetaRendererNativeSwapBuffers,
                            "Onscreen (swap-buffers)");
@@ -1157,12 +1158,47 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
   if (egl_context_changed)
     _cogl_winsys_egl_ensure_current (cogl_display);
 
-  kms_crtc = meta_crtc_kms_get_kms_crtc (META_CRTC_KMS (onscreen_native->crtc));
-  kms_device = meta_kms_crtc_get_device (kms_crtc);
+  rectangles_size = n_rectangles * 4 * sizeof (int);
+  onscreen_native->next_post.rectangles =
+    g_realloc (onscreen_native->next_post.rectangles, rectangles_size);
+  memcpy (onscreen_native->next_post.rectangles, rectangles, rectangles_size);
+  onscreen_native->next_post.n_rectangles = n_rectangles;
+
+  g_clear_pointer (&onscreen_native->next_post.frame, clutter_frame_unref);
+  onscreen_native->next_post.frame = clutter_frame_ref (frame);
+
+  post_latest_swap (onscreen);
+}
+
+static void
+post_latest_swap (CoglOnscreen *onscreen)
+{
+  CoglFramebuffer *framebuffer = COGL_FRAMEBUFFER (onscreen);
+  CoglContext *cogl_context = cogl_framebuffer_get_context (framebuffer);
+  CoglRenderer *cogl_renderer = cogl_context->display->renderer;
+  CoglRendererEGL *cogl_renderer_egl = cogl_renderer->winsys;
+  MetaRendererNativeGpuData *renderer_gpu_data = cogl_renderer_egl->platform;
+  MetaRendererNative *renderer_native = renderer_gpu_data->renderer_native;
+  MetaRenderer *renderer = META_RENDERER (renderer_native);
+  MetaBackend *backend = meta_renderer_get_backend (renderer);
+  MetaMonitorManager *monitor_manager =
+    meta_backend_get_monitor_manager (backend);
+  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
+  MetaPowerSave power_save_mode;
+  MetaCrtcKms *crtc_kms = META_CRTC_KMS (onscreen_native->crtc);
+  MetaKmsCrtc *kms_crtc = meta_crtc_kms_get_kms_crtc (crtc_kms);
+  MetaKmsDevice *kms_device = meta_kms_crtc_get_device (kms_crtc);
+  MetaKmsUpdate *kms_update;
+  g_autoptr (MetaKmsFeedback) kms_feedback = NULL;
+  g_autoptr (ClutterFrame) frame =
+    g_steal_pointer (&onscreen_native->next_post.frame);
+  MetaFrameNative *frame_native;
 
   power_save_mode = meta_monitor_manager_get_power_save_mode (monitor_manager);
   if (power_save_mode == META_POWER_SAVE_ON)
     {
+      frame_native = meta_frame_native_from_frame (frame);
+
       kms_update = meta_frame_native_ensure_kms_update (frame_native,
                                                         kms_device);
       meta_kms_update_add_result_listener (kms_update,
@@ -1177,8 +1213,8 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
                                       onscreen_native->crtc,
                                       kms_update,
                                       META_KMS_PAGE_FLIP_LISTENER_FLAG_NONE,
-                                      rectangles,
-                                      n_rectangles);
+                                      onscreen_native->next_post.rectangles,
+                                      onscreen_native->next_post.n_rectangles);
     }
   else
     {
@@ -2443,6 +2479,10 @@ meta_onscreen_native_dispose (GObject *object)
 
   g_clear_object (&onscreen_native->output);
   g_clear_object (&onscreen_native->crtc);
+
+  g_clear_pointer (&onscreen_native->next_post.rectangles, g_free);
+  g_clear_pointer (&onscreen_native->next_post.frame, clutter_frame_unref);
+  onscreen_native->next_post.n_rectangles = 0;
 }
 
 static void
-- 
GitLab

From d0f2786aa5c306ac7fe51136de1ada16aac7a5b5 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 28 Oct 2021 17:24:11 +0800
Subject: [PATCH 21/42] onscreen/native: Add a missing frame notification

In the unlikely event that swap_buffers_with_damage drops the previous swap
it was forgetting to notify about the discarded frame. That could lead to
frame clock freezes.
---
 src/backends/native/meta-onscreen-native.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 50395ea070c..6c5a39ea41f 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -1133,6 +1133,15 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
     {
     case META_RENDERER_NATIVE_MODE_GBM:
       g_warn_if_fail (onscreen_native->gbm.next_fb == NULL);
+      if (onscreen_native->gbm.next_fb != NULL)
+        {
+          CoglFrameInfo *frame_info;
+
+          frame_info = cogl_onscreen_peek_head_frame_info (onscreen);
+          frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
+          meta_onscreen_native_notify_frame_complete (onscreen);
+        }
+
       if (onscreen_native->secondary_gpu_state)
         g_set_object (&onscreen_native->gbm.next_fb, secondary_gpu_fb);
       else
-- 
GitLab

From b1332f3517c2f0dfb28c9bb9b1bb749a0287cc40 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 17 Sep 2021 17:59:28 +0800
Subject: [PATCH 22/42] onscreen/native: Defer posting if there's already a
 post in progress

And when the number of pending posts decreases we know it's safe to submit
a new one. Since KMS generally only supports one outstanding post right now,
"decreases" means equal to zero.
---
 src/backends/native/meta-onscreen-native.c | 161 ++++++++++++++++++---
 1 file changed, 141 insertions(+), 20 deletions(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 6c5a39ea41f..c8469281056 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -94,6 +94,7 @@ struct _MetaOnscreenNative
   struct {
     struct gbm_surface *surface;
     MetaDrmBuffer *next_fb;
+    MetaDrmBuffer *stalled_fb;
 
     /* Temporary workaround for the scanout-failed signal wanting the buffer
      * to live longer than it does, and then it doesn't use it anyway...
@@ -121,6 +122,8 @@ struct _MetaOnscreenNative
   gulong color_space_changed_handler_id;
   gulong hdr_metadata_changed_handler_id;
 
+  unsigned int swaps_pending;
+
   struct {
     int *rectangles;  /* 4 x n_rectangles */
     int n_rectangles;
@@ -134,7 +137,11 @@ G_DEFINE_TYPE (MetaOnscreenNative, meta_onscreen_native,
 static GQuark blit_source_quark = 0;
 
 static void
-post_latest_swap (CoglOnscreen *onscreen);
+try_post_latest_swap (CoglOnscreen *onscreen);
+
+static void
+post_finish_frame (MetaOnscreenNative *onscreen_native,
+                   MetaKmsUpdate      *kms_update);
 
 static gboolean
 init_secondary_gpu_state (MetaRendererNative  *renderer_native,
@@ -212,6 +219,7 @@ notify_view_crtc_presented (MetaRendererView *view,
 
   meta_onscreen_native_notify_frame_complete (onscreen);
   meta_swap_chain_swap_buffers (meta_kms_crtc_get_swap_chain (kms_crtc));
+  try_post_latest_swap (onscreen);
 }
 
 static void
@@ -261,15 +269,13 @@ page_flip_feedback_ready (MetaKmsCrtc *kms_crtc,
   CoglFramebuffer *framebuffer =
     clutter_stage_view_get_onscreen (CLUTTER_STAGE_VIEW (view));
   CoglOnscreen *onscreen = COGL_ONSCREEN (framebuffer);
-  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
   CoglFrameInfo *frame_info;
 
   frame_info = cogl_onscreen_peek_head_frame_info (onscreen);
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
 
-  g_warn_if_fail (!onscreen_native->gbm.next_fb);
-
   meta_onscreen_native_notify_frame_complete (onscreen);
+  try_post_latest_swap (onscreen);
 }
 
 static void
@@ -319,6 +325,7 @@ page_flip_feedback_discarded (MetaKmsCrtc  *kms_crtc,
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
 
   meta_onscreen_native_notify_frame_complete (onscreen);
+  try_post_latest_swap (onscreen);
 }
 
 static const MetaKmsPageFlipListenerVtable page_flip_listener_vtable = {
@@ -379,19 +386,40 @@ custom_egl_stream_page_flip (gpointer custom_page_flip_data,
 }
 #endif /* HAVE_EGL_DEVICE */
 
-void
-meta_onscreen_native_dummy_power_save_page_flip (CoglOnscreen *onscreen)
+static void
+drop_stalled_swap (CoglOnscreen *onscreen)
 {
   CoglFrameInfo *frame_info;
   MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
 
-  g_clear_object (&onscreen_native->gbm.next_fb);
+  /* Remember we can't compare stalled_fb because it's not used by
+   * META_RENDERER_NATIVE_MODE_EGL_DEVICE. So we judge stalled to be whenever
+   * swaps_pending > 1.
+   */
+  if (onscreen_native->swaps_pending <= 1)
+    return;
+
+  onscreen_native->swaps_pending--;
+
+  g_clear_object (&onscreen_native->gbm.stalled_fb);
 
   frame_info = cogl_onscreen_peek_tail_frame_info (onscreen);
   frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
   meta_onscreen_native_notify_frame_complete (onscreen);
 }
 
+void
+meta_onscreen_native_dummy_power_save_page_flip (CoglOnscreen *onscreen)
+{
+  drop_stalled_swap (onscreen);
+
+  /* If the monitor just woke up and the shell is fully idle (has nothing
+   * more to swap) then we just woke to an indefinitely black screen. Let's
+   * fix that using the last swap (which is never classified as "stalled").
+   */
+  try_post_latest_swap (onscreen);
+}
+
 static void
 meta_onscreen_native_flip_crtc (CoglOnscreen                *onscreen,
                                 MetaRendererView            *view,
@@ -1024,9 +1052,15 @@ swap_buffer_result_feedback (const MetaKmsFeedback *kms_feedback,
     g_warning ("Page flip failed: %s", error->message);
 
   frame_info = cogl_onscreen_peek_head_frame_info (onscreen);
-  frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
 
-  meta_onscreen_native_notify_frame_complete (onscreen);
+  /* After resuming from suspend, drop_stalled_swap might have done this
+   * already and emptied the frame_info queue.
+   */
+  if (frame_info)
+    {
+      frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
+      meta_onscreen_native_notify_frame_complete (onscreen);
+    }
 }
 
 static const MetaKmsResultListenerVtable swap_buffer_result_listener_vtable = {
@@ -1132,14 +1166,13 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
   switch (renderer_gpu_data->mode)
     {
     case META_RENDERER_NATIVE_MODE_GBM:
-      g_warn_if_fail (onscreen_native->gbm.next_fb == NULL);
       if (onscreen_native->gbm.next_fb != NULL)
         {
-          CoglFrameInfo *frame_info;
-
-          frame_info = cogl_onscreen_peek_head_frame_info (onscreen);
-          frame_info->flags |= COGL_FRAME_INFO_FLAG_SYMBOLIC;
-          meta_onscreen_native_notify_frame_complete (onscreen);
+          g_warn_if_fail (onscreen_native->gbm.stalled_fb == NULL);
+          drop_stalled_swap (onscreen);
+          g_assert (onscreen_native->gbm.stalled_fb == NULL);
+          onscreen_native->gbm.stalled_fb =
+            g_steal_pointer (&onscreen_native->gbm.next_fb);
         }
 
       if (onscreen_native->secondary_gpu_state)
@@ -1176,11 +1209,12 @@ meta_onscreen_native_swap_buffers_with_damage (CoglOnscreen  *onscreen,
   g_clear_pointer (&onscreen_native->next_post.frame, clutter_frame_unref);
   onscreen_native->next_post.frame = clutter_frame_ref (frame);
 
-  post_latest_swap (onscreen);
+  onscreen_native->swaps_pending++;
+  try_post_latest_swap (onscreen);
 }
 
 static void
-post_latest_swap (CoglOnscreen *onscreen)
+try_post_latest_swap (CoglOnscreen *onscreen)
 {
   CoglFramebuffer *framebuffer = COGL_FRAMEBUFFER (onscreen);
   CoglContext *cogl_context = cogl_framebuffer_get_context (framebuffer);
@@ -1199,15 +1233,41 @@ post_latest_swap (CoglOnscreen *onscreen)
   MetaKmsDevice *kms_device = meta_kms_crtc_get_device (kms_crtc);
   MetaKmsUpdate *kms_update;
   g_autoptr (MetaKmsFeedback) kms_feedback = NULL;
-  g_autoptr (ClutterFrame) frame =
-    g_steal_pointer (&onscreen_native->next_post.frame);
+  g_autoptr (ClutterFrame) frame = NULL;
   MetaFrameNative *frame_native;
 
+  if (onscreen_native->next_post.frame == NULL)
+    return;
+
   power_save_mode = meta_monitor_manager_get_power_save_mode (monitor_manager);
   if (power_save_mode == META_POWER_SAVE_ON)
     {
+      unsigned int frames_pending =
+        cogl_onscreen_count_pending_frames (onscreen);
+      unsigned int posts_pending;
+
+      g_assert (frames_pending >= onscreen_native->swaps_pending);
+      posts_pending = frames_pending - onscreen_native->swaps_pending;
+      if (posts_pending > 0)
+        return;  /* wait for the next frame notification and then try again */
+
+      frame = g_steal_pointer (&onscreen_native->next_post.frame);
       frame_native = meta_frame_native_from_frame (frame);
 
+      if (onscreen_native->swaps_pending == 0)
+        {
+          if (frame_native)
+            {
+              kms_update = meta_frame_native_steal_kms_update (frame_native);
+              if (kms_update)
+                post_finish_frame (onscreen_native, kms_update);
+            }
+          return;
+        }
+
+      drop_stalled_swap (onscreen);
+      onscreen_native->swaps_pending--;
+
       kms_update = meta_frame_native_ensure_kms_update (frame_native,
                                                         kms_device);
       meta_kms_update_add_result_listener (kms_update,
@@ -1408,6 +1468,18 @@ meta_onscreen_native_direct_scanout (CoglOnscreen   *onscreen,
       return FALSE;
     }
 
+  /* Our direct scanout frame counts as 1, so more than that means we would
+   * be jumping the queue (and post would fail).
+   */
+  if (cogl_onscreen_count_pending_frames (onscreen) > 1)
+    {
+      g_set_error_literal (error,
+                           COGL_SCANOUT_ERROR,
+                           COGL_SCANOUT_ERROR_INHIBITED,
+                           "Direct scanout is inhibited during triple buffering");
+      return FALSE;
+    }
+
   renderer_gpu_data = meta_renderer_native_get_gpu_data (renderer_native,
                                                          render_gpu);
 
@@ -1589,6 +1661,20 @@ meta_onscreen_native_finish_frame (CoglOnscreen *onscreen,
   MetaFrameNative *frame_native = meta_frame_native_from_frame (frame);
   MetaKmsUpdate *kms_update;
 
+  if (meta_frame_native_has_kms_update (frame_native) &&
+      cogl_onscreen_count_pending_frames (onscreen) > 0 &&
+      onscreen_native->swaps_pending == 0)
+    {
+      /* Posts are busy AND we have no swaps pending so just retry the same
+       * frame later in try_post_latest_swap.
+       */
+      g_warn_if_fail (onscreen_native->next_post.frame == NULL);
+      g_clear_pointer (&onscreen_native->next_post.frame, clutter_frame_unref);
+      onscreen_native->next_post.frame = clutter_frame_ref (frame);
+      clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
+      return;
+    }
+
   kms_update = meta_frame_native_steal_kms_update (frame_native);
   if (!kms_update)
     {
@@ -1604,6 +1690,42 @@ meta_onscreen_native_finish_frame (CoglOnscreen *onscreen,
         }
     }
 
+  if (cogl_onscreen_count_pending_frames (onscreen) > 0)
+    {
+      /* Posts are busy AND we have swaps pending so best to merge our cursor
+       * update into the pending swap.
+       */
+      MetaFrameNative *older_frame_native;
+      MetaKmsUpdate *older_kms_update;
+
+      g_return_if_fail (onscreen_native->swaps_pending > 0);
+      g_return_if_fail (onscreen_native->next_post.frame != NULL);
+
+      older_frame_native =
+        meta_frame_native_from_frame (onscreen_native->next_post.frame);
+      older_kms_update =
+        meta_frame_native_ensure_kms_update (older_frame_native, kms_device);
+      meta_kms_update_merge_from (older_kms_update, kms_update);
+      meta_kms_update_free (kms_update);
+
+      clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_IDLE);
+      return;
+    }
+
+  post_finish_frame (onscreen_native, kms_update);
+
+  clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
+}
+
+static void
+post_finish_frame (MetaOnscreenNative *onscreen_native,
+                   MetaKmsUpdate      *kms_update)
+{
+  MetaCrtc *crtc = onscreen_native->crtc;
+  MetaKmsCrtc *kms_crtc = meta_crtc_kms_get_kms_crtc (META_CRTC_KMS (crtc));
+  MetaKmsDevice *kms_device = meta_kms_crtc_get_device (kms_crtc);
+  g_autoptr (MetaKmsFeedback) kms_feedback = NULL;
+
   meta_kms_update_add_result_listener (kms_update,
                                        &finish_frame_result_listener_vtable,
                                        NULL,
@@ -1627,7 +1749,6 @@ meta_onscreen_native_finish_frame (CoglOnscreen *onscreen,
   meta_kms_update_set_flushing (kms_update, kms_crtc);
   meta_kms_device_post_update (kms_device, kms_update,
                                META_KMS_UPDATE_FLAG_NONE);
-  clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
 }
 
 static gboolean
-- 
GitLab

From db13779e76509d47f0585bdb921db0950cfbd2c4 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 9 Dec 2022 14:22:31 +0800
Subject: [PATCH 23/42] onscreen/native: Increase secondary GPU dumb_fbs from 2
 to 3

So that they don't get overwritten prematurely during triple buffering
causing tearing.

https://launchpad.net/bugs/1999216
---
 src/backends/native/meta-onscreen-native.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index c8469281056..8ed56c5d5fb 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -72,7 +72,7 @@ typedef struct _MetaOnscreenNativeSecondaryGpuState
 
   struct {
     MetaDrmBufferDumb *current_dumb_fb;
-    MetaDrmBufferDumb *dumb_fbs[2];
+    MetaDrmBufferDumb *dumb_fbs[3];
   } cpu;
 
   gboolean noted_primary_gpu_copy_ok;
@@ -716,12 +716,17 @@ static MetaDrmBufferDumb *
 secondary_gpu_get_next_dumb_buffer (MetaOnscreenNativeSecondaryGpuState *secondary_gpu_state)
 {
   MetaDrmBufferDumb *current_dumb_fb;
+  const int n_dumb_fbs = G_N_ELEMENTS (secondary_gpu_state->cpu.dumb_fbs);
+  int i;
 
   current_dumb_fb = secondary_gpu_state->cpu.current_dumb_fb;
-  if (current_dumb_fb == secondary_gpu_state->cpu.dumb_fbs[0])
-    return secondary_gpu_state->cpu.dumb_fbs[1];
-  else
-    return secondary_gpu_state->cpu.dumb_fbs[0];
+  for (i = 0; i < n_dumb_fbs; i++)
+    {
+      if (current_dumb_fb == secondary_gpu_state->cpu.dumb_fbs[i])
+        return secondary_gpu_state->cpu.dumb_fbs[(i + 1) % n_dumb_fbs];
+    }
+
+  return secondary_gpu_state->cpu.dumb_fbs[0];
 }
 
 static MetaDrmBuffer *
-- 
GitLab

From 80198e941417f381b2bca8070740a2b2124d119b Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 4 Nov 2021 16:09:26 +0800
Subject: [PATCH 24/42] onscreen/native: Add function
 meta_onscreen_native_discard_pending_swaps

---
 src/backends/native/meta-onscreen-native.c | 11 +++++++++++
 src/backends/native/meta-onscreen-native.h |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 8ed56c5d5fb..1b0ffdf7eca 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -1756,6 +1756,17 @@ post_finish_frame (MetaOnscreenNative *onscreen_native,
                                META_KMS_UPDATE_FLAG_NONE);
 }
 
+void
+meta_onscreen_native_discard_pending_swaps (CoglOnscreen *onscreen)
+{
+  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
+
+  onscreen_native->swaps_pending = 0;
+
+  g_clear_object (&onscreen_native->gbm.stalled_fb);
+  g_clear_object (&onscreen_native->gbm.next_fb);
+}
+
 static gboolean
 should_surface_be_sharable (CoglOnscreen *onscreen)
 {
diff --git a/src/backends/native/meta-onscreen-native.h b/src/backends/native/meta-onscreen-native.h
index 3be01a33eb3..575da2282b8 100644
--- a/src/backends/native/meta-onscreen-native.h
+++ b/src/backends/native/meta-onscreen-native.h
@@ -47,6 +47,8 @@ void meta_onscreen_native_finish_frame (CoglOnscreen *onscreen,
 
 void meta_onscreen_native_dummy_power_save_page_flip (CoglOnscreen *onscreen);
 
+void meta_onscreen_native_discard_pending_swaps (CoglOnscreen *onscreen);
+
 gboolean meta_onscreen_native_is_buffer_scanout_compatible (CoglOnscreen  *onscreen,
                                                             MetaDrmBuffer *fb);
 
-- 
GitLab

From 5af2e7e432a8e921976e253661a0a9495617f4dd Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Wed, 11 May 2022 16:00:32 +0800
Subject: [PATCH 25/42] onscreen/native: Skip try_post_latest_swap if shutting
 down

Otherwise we could get:

meta_kms_prepare_shutdown ->
  flush_callbacks ->
  ... ->
  try_post_latest_swap ->
  post and queue more callbacks

So later in shutdown those callbacks would trigger an assertion failure
in meta_kms_impl_device_atomic_finalize:

g_hash_table_size (impl_device_atomic->page_flip_datas) == 0

Also remember to discard_pending_swaps to break the circular reference
between MetaOnscreenNative and its next_fb caused by the association
"gbm_surface owner". Or else that would trigger another assertion failure:

meta_device_pool_finalize: runtime check failed: (!pool->files)
---
 src/backends/native/meta-onscreen-native.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 1b0ffdf7eca..274245bd301 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -1229,6 +1229,8 @@ try_post_latest_swap (CoglOnscreen *onscreen)
   MetaRendererNative *renderer_native = renderer_gpu_data->renderer_native;
   MetaRenderer *renderer = META_RENDERER (renderer_native);
   MetaBackend *backend = meta_renderer_get_backend (renderer);
+  MetaBackendNative *backend_native = META_BACKEND_NATIVE (backend);
+  MetaKms *kms = meta_backend_native_get_kms (backend_native);
   MetaMonitorManager *monitor_manager =
     meta_backend_get_monitor_manager (backend);
   MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
@@ -1244,6 +1246,12 @@ try_post_latest_swap (CoglOnscreen *onscreen)
   if (onscreen_native->next_post.frame == NULL)
     return;
 
+  if (meta_kms_is_shutting_down (kms))
+    {
+      meta_onscreen_native_discard_pending_swaps (onscreen);
+      return;
+    }
+
   power_save_mode = meta_monitor_manager_get_power_save_mode (monitor_manager);
   if (power_save_mode == META_POWER_SAVE_ON)
     {
-- 
GitLab

From 68845a678a97336d4d26e56a4bb2360f61a48db2 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 4 Nov 2021 16:09:52 +0800
Subject: [PATCH 26/42] renderer/native: Discard pending swaps when rebuilding
 views

It's analogous to discard_pending_page_flips but represents swaps that
might become flips after the next frame notification callbacks, thanks
to triple buffering. Since the views are being rebuilt and their onscreens
are about to be destroyed, turning those swaps into more flips/posts would
just lead to unexpected behaviour (like trying to flip on a half-destroyed
inactive CRTC).
---
 src/backends/native/meta-renderer-native.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index a9c5e73f46e..7c97593e033 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -1501,6 +1501,26 @@ detach_onscreens (MetaRenderer *renderer)
     }
 }
 
+static void
+discard_pending_swaps (MetaRenderer *renderer)
+{
+  GList *views = meta_renderer_get_views (renderer);;
+  GList *l;
+
+  for (l = views; l; l = l->next)
+    {
+      ClutterStageView *stage_view = l->data;
+      CoglFramebuffer *fb = clutter_stage_view_get_onscreen (stage_view);
+      CoglOnscreen *onscreen;
+
+      if (!COGL_IS_ONSCREEN (fb))
+        continue;
+
+      onscreen = COGL_ONSCREEN (fb);
+      meta_onscreen_native_discard_pending_swaps (onscreen);
+    }
+}
+
 static void
 meta_renderer_native_rebuild_views (MetaRenderer *renderer)
 {
@@ -1511,6 +1531,7 @@ meta_renderer_native_rebuild_views (MetaRenderer *renderer)
   MetaRendererClass *parent_renderer_class =
     META_RENDERER_CLASS (meta_renderer_native_parent_class);
 
+  discard_pending_swaps (renderer);
   meta_kms_discard_pending_page_flips (kms);
   g_hash_table_remove_all (renderer_native->mode_set_updates);
 
-- 
GitLab

From a87adbc2d7bc4f0762c2204013c3983ccfcb64ab Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 10 Aug 2021 17:46:49 +0800
Subject: [PATCH 27/42] clutter/frame-clock: Lower the threshold for disabling
 error diffusion

Error diffusion was introduced in 0555a5bbc15 for Nvidia where last
presentation time is always unknown (zero). Dispatch times would drift
apart always being a fraction of a frame late, and accumulated to cause
periodic frame skips. So error diffusion corrected that precisely and
avoided the skips.

That works great with double buffering but less great with triple
buffering. It's certainly still needed with triple buffering but
correcting for a lateness of many milliseconds isn't a good idea. That's
because a dispatch being that late is not due to main loop jitter but due
to Nvidia's swap buffers blocking when the queue is full. So scheduling
the next frame even earlier using last_dispatch_lateness_us would just
perpetuate the problem of swap buffers blocking for too long.

So now we lower the threshold of when error diffusion gets disabled. It's
still high enough to fix the original smoothness problem it was for, but
now low enough to detect Nvidia's occasionally blocking swaps and backs
off in that case.

Since the average duration of a blocking swap is half a frame interval
and we want to distinguish between that and sub-millisecond jitter, the
logical threshold is halfway again: refresh_interval_us/4.
---
 clutter/clutter/clutter-frame-clock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index 8d5742836b9..24fe4f6e7b4 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -734,7 +734,7 @@ clutter_frame_clock_dispatch (ClutterFrameClock *frame_clock,
                              frame_clock->refresh_interval_us;
 
   lateness_us = time_us - ideal_dispatch_time_us;
-  if (lateness_us < 0 || lateness_us >= frame_clock->refresh_interval_us)
+  if (lateness_us < 0 || lateness_us >= frame_clock->refresh_interval_us / 4)
     frame_clock->last_dispatch_lateness_us = 0;
   else
     frame_clock->last_dispatch_lateness_us = lateness_us;
-- 
GitLab

From b7df5ebcade7b83fdfe6cac6fdaeb9dcd5eab9d6 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 24 Jul 2020 14:13:11 +0800
Subject: [PATCH 28/42] clutter/frame-clock: Merge states DISPATCHING and
 PENDING_PRESENTED

Chronologically they already overlap in time as presentation may
complete in the middle of the dispatch function, otherwise they are
contiguous in time. And most switch statements treated the two states
the same already so they're easy to merge into a single `DISPATCHED`
state.

Having fewer states now will make life easier when we add more states
later.
---
 clutter/clutter/clutter-frame-clock.c | 28 ++++++++++-----------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index 24fe4f6e7b4..5ed3e40251d 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -55,8 +55,7 @@ typedef enum _ClutterFrameClockState
   CLUTTER_FRAME_CLOCK_STATE_INIT,
   CLUTTER_FRAME_CLOCK_STATE_IDLE,
   CLUTTER_FRAME_CLOCK_STATE_SCHEDULED,
-  CLUTTER_FRAME_CLOCK_STATE_DISPATCHING,
-  CLUTTER_FRAME_CLOCK_STATE_PENDING_PRESENTED,
+  CLUTTER_FRAME_CLOCK_STATE_DISPATCHED,
 } ClutterFrameClockState;
 
 struct _ClutterFrameClock
@@ -378,8 +377,7 @@ clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
       g_warn_if_reached ();
       break;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHING:
-    case CLUTTER_FRAME_CLOCK_STATE_PENDING_PRESENTED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
       frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_IDLE;
       maybe_reschedule_update (frame_clock);
       break;
@@ -398,8 +396,7 @@ clutter_frame_clock_notify_ready (ClutterFrameClock *frame_clock)
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
       g_warn_if_reached ();
       break;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHING:
-    case CLUTTER_FRAME_CLOCK_STATE_PENDING_PRESENTED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
       frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_IDLE;
       maybe_reschedule_update (frame_clock);
       break;
@@ -613,8 +610,7 @@ clutter_frame_clock_inhibit (ClutterFrameClock *frame_clock)
           frame_clock->pending_reschedule = TRUE;
           frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_IDLE;
           break;
-        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHING:
-        case CLUTTER_FRAME_CLOCK_STATE_PENDING_PRESENTED:
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
           break;
         }
 
@@ -652,8 +648,7 @@ clutter_frame_clock_schedule_update_now (ClutterFrameClock *frame_clock)
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
       next_update_time_us = g_get_monotonic_time ();
       break;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHING:
-    case CLUTTER_FRAME_CLOCK_STATE_PENDING_PRESENTED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
       frame_clock->pending_reschedule = TRUE;
       frame_clock->pending_reschedule_now = TRUE;
       return;
@@ -693,8 +688,7 @@ clutter_frame_clock_schedule_update (ClutterFrameClock *frame_clock)
       break;
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
       return;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHING:
-    case CLUTTER_FRAME_CLOCK_STATE_PENDING_PRESENTED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
       frame_clock->pending_reschedule = TRUE;
       return;
     }
@@ -756,7 +750,7 @@ clutter_frame_clock_dispatch (ClutterFrameClock *frame_clock,
   frame_clock->last_dispatch_time_us = time_us;
   g_source_set_ready_time (frame_clock->source, -1);
 
-  frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHING;
+  frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED;
 
   frame_count = frame_clock->frame_count++;
 
@@ -788,19 +782,19 @@ clutter_frame_clock_dispatch (ClutterFrameClock *frame_clock,
   switch (frame_clock->state)
     {
     case CLUTTER_FRAME_CLOCK_STATE_INIT:
-    case CLUTTER_FRAME_CLOCK_STATE_PENDING_PRESENTED:
       g_warn_if_reached ();
       break;
     case CLUTTER_FRAME_CLOCK_STATE_IDLE:
+      /* Presentation completed synchronously in the above listener */
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
       break;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHING:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
       switch (result)
         {
         case CLUTTER_FRAME_RESULT_PENDING_PRESENTED:
-          frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_PENDING_PRESENTED;
           break;
         case CLUTTER_FRAME_RESULT_IDLE:
+          /* The frame was aborted; nothing to paint/present */
           frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_IDLE;
           maybe_reschedule_update (frame_clock);
           break;
@@ -933,8 +927,6 @@ clutter_frame_clock_dispose (GObject *object)
 {
   ClutterFrameClock *frame_clock = CLUTTER_FRAME_CLOCK (object);
 
-  g_warn_if_fail (frame_clock->state != CLUTTER_FRAME_CLOCK_STATE_DISPATCHING);
-
   if (frame_clock->source)
     {
       g_signal_emit (frame_clock, signals[DESTROY], 0);
-- 
GitLab

From 86ddb32b6a18bca7be372d11b925b46195cf5964 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Mon, 13 Dec 2021 17:03:44 +0800
Subject: [PATCH 29/42] clutter/frame-clock: Don't clamp measurements

Because values over refresh_interval_us are real and valid. They
tell us when we're not keeping up.

This reverts commit 9c021b0bc2e4f0d2698f36db41224645ed31b6dc.
---
 clutter/clutter/clutter-frame-clock.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index 5ed3e40251d..a94d474e268 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -348,10 +348,9 @@ clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
                     swap_to_flip_us);
 
       frame_clock->shortterm_max_update_duration_us =
-        CLAMP (frame_clock->last_dispatch_lateness_us + dispatch_to_swap_us +
-               MAX (swap_to_rendering_done_us, swap_to_flip_us),
-               frame_clock->shortterm_max_update_duration_us,
-               frame_clock->refresh_interval_us);
+        MAX (frame_clock->shortterm_max_update_duration_us,
+             frame_clock->last_dispatch_lateness_us + dispatch_to_swap_us +
+             MAX (swap_to_rendering_done_us, swap_to_flip_us));
 
       maybe_update_longterm_max_duration_us (frame_clock, frame_info);
 
@@ -434,8 +433,6 @@ clutter_frame_clock_compute_max_render_time_us (ClutterFrameClock *frame_clock)
     frame_clock->vblank_duration_us +
     clutter_max_render_time_constant_us;
 
-  max_render_time_us = CLAMP (max_render_time_us, 0, refresh_interval_us);
-
   return max_render_time_us;
 }
 
-- 
GitLab

From 48682ee59ee04760976160814c800db595efd8b5 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 10 Sep 2020 16:34:53 +0800
Subject: [PATCH 30/42] clutter/frame-clock: Add triple buffering support

---
 clutter/clutter/clutter-frame-clock.c | 159 +++++++++++++++++++++-----
 1 file changed, 133 insertions(+), 26 deletions(-)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index a94d474e268..8b731e48d15 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -55,7 +55,9 @@ typedef enum _ClutterFrameClockState
   CLUTTER_FRAME_CLOCK_STATE_INIT,
   CLUTTER_FRAME_CLOCK_STATE_IDLE,
   CLUTTER_FRAME_CLOCK_STATE_SCHEDULED,
-  CLUTTER_FRAME_CLOCK_STATE_DISPATCHED,
+  CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE,
+  CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED,
+  CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO,
 } ClutterFrameClockState;
 
 struct _ClutterFrameClock
@@ -72,6 +74,7 @@ struct _ClutterFrameClock
 
   ClutterFrameClockState state;
   int64_t last_dispatch_time_us;
+  int64_t prev_last_dispatch_time_us;
   int64_t last_dispatch_lateness_us;
   int64_t last_presentation_time_us;
   int64_t next_update_time_us;
@@ -86,6 +89,7 @@ struct _ClutterFrameClock
   int64_t vblank_duration_us;
   /* Last KMS buffer submission time. */
   int64_t last_flip_time_us;
+  int64_t prev_last_flip_time_us;
 
   /* Last time we promoted short-term maximum to long-term one */
   int64_t longterm_promotion_us;
@@ -330,14 +334,33 @@ clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
   if (frame_info->cpu_time_before_buffer_swap_us != 0)
     {
       int64_t dispatch_to_swap_us, swap_to_rendering_done_us, swap_to_flip_us;
+      int64_t dispatch_time_us = 0, flip_time_us = 0;
+
+      switch (frame_clock->state)
+        {
+        case CLUTTER_FRAME_CLOCK_STATE_INIT:
+        case CLUTTER_FRAME_CLOCK_STATE_IDLE:
+        case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
+          g_warn_if_reached ();
+          G_GNUC_FALLTHROUGH;
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
+          dispatch_time_us = frame_clock->last_dispatch_time_us;
+          flip_time_us = frame_clock->last_flip_time_us;
+          break;
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
+          dispatch_time_us = frame_clock->prev_last_dispatch_time_us;
+          flip_time_us = frame_clock->prev_last_flip_time_us;
+          break;
+        }
 
       dispatch_to_swap_us =
         frame_info->cpu_time_before_buffer_swap_us -
-        frame_clock->last_dispatch_time_us;
+        dispatch_time_us;
       swap_to_rendering_done_us =
         frame_info->gpu_rendering_duration_ns / 1000;
       swap_to_flip_us =
-        frame_clock->last_flip_time_us -
+        flip_time_us -
         frame_info->cpu_time_before_buffer_swap_us;
 
       CLUTTER_NOTE (FRAME_TIMINGS,
@@ -376,10 +399,18 @@ clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
       g_warn_if_reached ();
       break;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
       frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_IDLE;
       maybe_reschedule_update (frame_clock);
       break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_SCHEDULED;
+      maybe_reschedule_update (frame_clock);
+      break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE;
+      maybe_reschedule_update (frame_clock);
+      break;
     }
 }
 
@@ -395,10 +426,18 @@ clutter_frame_clock_notify_ready (ClutterFrameClock *frame_clock)
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
       g_warn_if_reached ();
       break;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
       frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_IDLE;
       maybe_reschedule_update (frame_clock);
       break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_SCHEDULED;
+      maybe_reschedule_update (frame_clock);
+      break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE;
+      maybe_reschedule_update (frame_clock);
+      break;
     }
 }
 
@@ -413,7 +452,14 @@ clutter_frame_clock_compute_max_render_time_us (ClutterFrameClock *frame_clock)
   if (!frame_clock->ever_got_measurements ||
       G_UNLIKELY (clutter_paint_debug_flags &
                   CLUTTER_DEBUG_DISABLE_DYNAMIC_MAX_RENDER_TIME))
-    return refresh_interval_us * SYNC_DELAY_FALLBACK_FRACTION;
+    {
+      int64_t ret = refresh_interval_us * SYNC_DELAY_FALLBACK_FRACTION;
+
+      if (frame_clock->state == CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE)
+        ret += refresh_interval_us;
+
+      return ret;
+    }
 
   /* Max render time shows how early the frame clock needs to be dispatched
    * to make it to the predicted next presentation time. It is an estimate of
@@ -447,7 +493,7 @@ calculate_next_update_time_us (ClutterFrameClock *frame_clock,
   int64_t refresh_interval_us;
   int64_t min_render_time_allowed_us;
   int64_t max_render_time_allowed_us;
-  int64_t next_presentation_time_us;
+  int64_t next_presentation_time_us = 0;
   int64_t next_update_time_us;
 
   now_us = g_get_monotonic_time ();
@@ -492,7 +538,24 @@ calculate_next_update_time_us (ClutterFrameClock *frame_clock,
    *
    */
   last_presentation_time_us = frame_clock->last_presentation_time_us;
-  next_presentation_time_us = last_presentation_time_us + refresh_interval_us;
+  switch (frame_clock->state)
+    {
+    case CLUTTER_FRAME_CLOCK_STATE_INIT:
+    case CLUTTER_FRAME_CLOCK_STATE_IDLE:
+    case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
+      next_presentation_time_us = last_presentation_time_us +
+                                  refresh_interval_us;
+      break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
+      next_presentation_time_us = last_presentation_time_us +
+                                  2 * refresh_interval_us;
+      break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
+      next_presentation_time_us = last_presentation_time_us +
+                                  3 * refresh_interval_us;
+      break;
+    }
 
   /*
    * However, the last presentation could have happened more than a frame ago.
@@ -607,7 +670,12 @@ clutter_frame_clock_inhibit (ClutterFrameClock *frame_clock)
           frame_clock->pending_reschedule = TRUE;
           frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_IDLE;
           break;
-        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
+          frame_clock->pending_reschedule = TRUE;
+          frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE;
+          break;
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
           break;
         }
 
@@ -644,8 +712,15 @@ clutter_frame_clock_schedule_update_now (ClutterFrameClock *frame_clock)
     case CLUTTER_FRAME_CLOCK_STATE_IDLE:
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
       next_update_time_us = g_get_monotonic_time ();
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_SCHEDULED;
       break;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
+      next_update_time_us = g_get_monotonic_time ();
+      frame_clock->state =
+        CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED;
+      break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
       frame_clock->pending_reschedule = TRUE;
       frame_clock->pending_reschedule_now = TRUE;
       return;
@@ -655,7 +730,6 @@ clutter_frame_clock_schedule_update_now (ClutterFrameClock *frame_clock)
 
   frame_clock->next_update_time_us = next_update_time_us;
   g_source_set_ready_time (frame_clock->source, next_update_time_us);
-  frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_SCHEDULED;
   frame_clock->is_next_presentation_time_valid = FALSE;
 }
 
@@ -674,6 +748,7 @@ clutter_frame_clock_schedule_update (ClutterFrameClock *frame_clock)
     {
     case CLUTTER_FRAME_CLOCK_STATE_INIT:
       next_update_time_us = g_get_monotonic_time ();
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_SCHEDULED;
       break;
     case CLUTTER_FRAME_CLOCK_STATE_IDLE:
       calculate_next_update_time_us (frame_clock,
@@ -682,10 +757,21 @@ clutter_frame_clock_schedule_update (ClutterFrameClock *frame_clock)
                                      &frame_clock->min_render_time_allowed_us);
       frame_clock->is_next_presentation_time_valid =
         (frame_clock->next_presentation_time_us != 0);
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_SCHEDULED;
       break;
     case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
       return;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
+      calculate_next_update_time_us (frame_clock,
+                                     &next_update_time_us,
+                                     &frame_clock->next_presentation_time_us,
+                                     &frame_clock->min_render_time_allowed_us);
+      frame_clock->is_next_presentation_time_valid =
+        (frame_clock->next_presentation_time_us != 0);
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED;
+      break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
       frame_clock->pending_reschedule = TRUE;
       return;
     }
@@ -694,7 +780,6 @@ clutter_frame_clock_schedule_update (ClutterFrameClock *frame_clock)
 
   frame_clock->next_update_time_us = next_update_time_us;
   g_source_set_ready_time (frame_clock->source, next_update_time_us);
-  frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_SCHEDULED;
 }
 
 static void
@@ -744,10 +829,25 @@ clutter_frame_clock_dispatch (ClutterFrameClock *frame_clock,
                     jitter_us * 100 / frame_clock->refresh_interval_us);
     }
 
+  frame_clock->prev_last_dispatch_time_us = frame_clock->last_dispatch_time_us;
   frame_clock->last_dispatch_time_us = time_us;
   g_source_set_ready_time (frame_clock->source, -1);
 
-  frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED;
+  switch (frame_clock->state)
+    {
+    case CLUTTER_FRAME_CLOCK_STATE_INIT:
+    case CLUTTER_FRAME_CLOCK_STATE_IDLE:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
+      g_warn_if_reached ();
+      return;
+    case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE;
+      break;
+    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
+      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO;
+      break;
+    }
 
   frame_count = frame_clock->frame_count++;
 
@@ -776,25 +876,31 @@ clutter_frame_clock_dispatch (ClutterFrameClock *frame_clock,
   result = iface->frame (frame_clock, frame, frame_clock->listener.user_data);
   COGL_TRACE_END (ClutterFrameClockFrame);
 
-  switch (frame_clock->state)
+  switch (result)
     {
-    case CLUTTER_FRAME_CLOCK_STATE_INIT:
-      g_warn_if_reached ();
-      break;
-    case CLUTTER_FRAME_CLOCK_STATE_IDLE:
-      /* Presentation completed synchronously in the above listener */
-    case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
+    case CLUTTER_FRAME_RESULT_PENDING_PRESENTED:
       break;
-    case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED:
-      switch (result)
+    case CLUTTER_FRAME_RESULT_IDLE:
+      /* The frame was aborted; nothing to paint/present */
+      switch (frame_clock->state)
         {
-        case CLUTTER_FRAME_RESULT_PENDING_PRESENTED:
+        case CLUTTER_FRAME_CLOCK_STATE_INIT:
+        case CLUTTER_FRAME_CLOCK_STATE_IDLE:
+        case CLUTTER_FRAME_CLOCK_STATE_SCHEDULED:
+          g_warn_if_reached ();
           break;
-        case CLUTTER_FRAME_RESULT_IDLE:
-          /* The frame was aborted; nothing to paint/present */
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
           frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_IDLE;
           maybe_reschedule_update (frame_clock);
           break;
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
+          frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_SCHEDULED;
+          maybe_reschedule_update (frame_clock);
+          break;
+        case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
+          frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE;
+          maybe_reschedule_update (frame_clock);
+          break;
         }
       break;
     }
@@ -830,6 +936,7 @@ void
 clutter_frame_clock_record_flip_time (ClutterFrameClock *frame_clock,
                                       int64_t            flip_time_us)
 {
+  frame_clock->prev_last_flip_time_us = frame_clock->last_flip_time_us;
   frame_clock->last_flip_time_us = flip_time_us;
 }
 
-- 
GitLab

From 59b2e140bdb5aaef647f9b6049fd25a96cdd55d0 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 10 Dec 2021 16:28:04 +0800
Subject: [PATCH 31/42] clutter/frame-clock: Log N-buffers in
 CLUTTTER_DEBUG=frame-timings

---
 clutter/clutter/clutter-frame-clock.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index 8b731e48d15..d50634ea0d7 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -252,6 +252,12 @@ void
 clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
                                       ClutterFrameInfo  *frame_info)
 {
+#ifdef CLUTTER_ENABLE_DEBUG
+  const char *debug_state =
+    frame_clock->state == CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO ?
+    "Triple buffering" : "Double buffering";
+#endif
+
   COGL_TRACE_BEGIN_SCOPED (ClutterFrameClockNotifyPresented,
                            "Frame Clock (presented)");
 
@@ -364,7 +370,8 @@ clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
         frame_info->cpu_time_before_buffer_swap_us;
 
       CLUTTER_NOTE (FRAME_TIMINGS,
-                    "update2dispatch %ld µs, dispatch2swap %ld µs, swap2render %ld µs, swap2flip %ld µs",
+                    "%s: update2dispatch %ld µs, dispatch2swap %ld µs, swap2render %ld µs, swap2flip %ld µs",
+                    debug_state,
                     frame_clock->last_dispatch_lateness_us,
                     dispatch_to_swap_us,
                     swap_to_rendering_done_us,
@@ -382,7 +389,8 @@ clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
     }
   else
     {
-      CLUTTER_NOTE (FRAME_TIMINGS, "update2dispatch %ld µs",
+      CLUTTER_NOTE (FRAME_TIMINGS, "%s: update2dispatch %ld µs",
+                    debug_state,
                     frame_clock->last_dispatch_lateness_us);
     }
 
-- 
GitLab

From aedc8a1dcd81c170f0ebc3179be3e4172439b1dc Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 7 Sep 2021 19:08:15 +0800
Subject: [PATCH 32/42] clutter/frame: Add ClutterFrameHint to ClutterFrame

This will allow the backend to provide performance hints to the frame
clock in future.
---
 clutter/clutter/clutter-frame-clock.h   |  6 ++++++
 clutter/clutter/clutter-frame-private.h |  1 +
 clutter/clutter/clutter-frame.c         | 13 +++++++++++++
 clutter/clutter/clutter-frame.h         |  7 +++++++
 4 files changed, 27 insertions(+)

diff --git a/clutter/clutter/clutter-frame-clock.h b/clutter/clutter/clutter-frame-clock.h
index 93ebc943867..b6650a5a053 100644
--- a/clutter/clutter/clutter-frame-clock.h
+++ b/clutter/clutter/clutter-frame-clock.h
@@ -33,6 +33,12 @@ typedef enum _ClutterFrameResult
   CLUTTER_FRAME_RESULT_IDLE,
 } ClutterFrameResult;
 
+typedef enum _ClutterFrameHint
+{
+  CLUTTER_FRAME_HINT_NONE                     = 0,
+  CLUTTER_FRAME_HINT_DIRECT_SCANOUT_ATTEMPTED = 1 << 0,
+} ClutterFrameHint;
+
 #define CLUTTER_TYPE_FRAME_CLOCK (clutter_frame_clock_get_type ())
 CLUTTER_EXPORT
 G_DECLARE_FINAL_TYPE (ClutterFrameClock, clutter_frame_clock,
diff --git a/clutter/clutter/clutter-frame-private.h b/clutter/clutter/clutter-frame-private.h
index 0a0226b0a54..55c76df72ea 100644
--- a/clutter/clutter/clutter-frame-private.h
+++ b/clutter/clutter/clutter-frame-private.h
@@ -34,6 +34,7 @@ struct _ClutterFrame
 
   gboolean has_result;
   ClutterFrameResult result;
+  ClutterFrameHint hints;
 };
 
 CLUTTER_EXPORT
diff --git a/clutter/clutter/clutter-frame.c b/clutter/clutter/clutter-frame.c
index 85baef274ea..413ce9c2b6f 100644
--- a/clutter/clutter/clutter-frame.c
+++ b/clutter/clutter/clutter-frame.c
@@ -113,3 +113,16 @@ clutter_frame_set_result (ClutterFrame       *frame,
   frame->result = result;
   frame->has_result = TRUE;
 }
+
+void
+clutter_frame_set_hint (ClutterFrame     *frame,
+                        ClutterFrameHint  hint)
+{
+  frame->hints |= hint;
+}
+
+ClutterFrameHint
+clutter_frame_get_hints (ClutterFrame *frame)
+{
+  return frame->hints;
+}
diff --git a/clutter/clutter/clutter-frame.h b/clutter/clutter/clutter-frame.h
index 1d5660d685e..0e7f618a4e3 100644
--- a/clutter/clutter/clutter-frame.h
+++ b/clutter/clutter/clutter-frame.h
@@ -54,4 +54,11 @@ void clutter_frame_set_result (ClutterFrame       *frame,
 CLUTTER_EXPORT
 gboolean clutter_frame_has_result (ClutterFrame *frame);
 
+CLUTTER_EXPORT
+void clutter_frame_set_hint (ClutterFrame     *frame,
+                             ClutterFrameHint  hint);
+
+CLUTTER_EXPORT
+ClutterFrameHint clutter_frame_get_hints (ClutterFrame *frame);
+
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (ClutterFrame, clutter_frame_unref)
-- 
GitLab

From 68e12f7ad78b2915ba0b4c93b7e591792d226c76 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 7 Sep 2021 19:10:26 +0800
Subject: [PATCH 33/42] backends: Flag that the frame attempted direct scanout

We need this hint whether direct scanout succeeds or fails because it's
the mechanism by which we will tell the clock to enforce double buffering,
thus making direct scanout possible on future frames. Triple buffering
will be disabled until such time that direct scanout is not being attempted.
---
 src/backends/meta-stage-impl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/backends/meta-stage-impl.c b/src/backends/meta-stage-impl.c
index 26a7531296b..a052549f780 100644
--- a/src/backends/meta-stage-impl.c
+++ b/src/backends/meta-stage-impl.c
@@ -772,6 +772,8 @@ meta_stage_impl_redraw_view (ClutterStageWindow *stage_window,
     {
       g_autoptr (GError) error = NULL;
 
+      clutter_frame_set_hint (frame, CLUTTER_FRAME_HINT_DIRECT_SCANOUT_ATTEMPTED);
+
       if (meta_stage_impl_scanout_view (stage_impl,
                                         stage_view,
                                         scanout,
-- 
GitLab

From 0b055d1125e8f1ff5928fc309caa2c5c69e4364f Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 7 Sep 2021 19:15:18 +0800
Subject: [PATCH 34/42] clutter: Pass ClutterFrameHint(s) to the frame clock

---
 clutter/clutter/clutter-frame-clock.c |  8 ++++++--
 clutter/clutter/clutter-frame-clock.h |  5 +++--
 clutter/clutter/clutter-stage-view.c  | 11 +++++++++--
 3 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index d50634ea0d7..1c714f85eb8 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -91,6 +91,8 @@ struct _ClutterFrameClock
   int64_t last_flip_time_us;
   int64_t prev_last_flip_time_us;
 
+  ClutterFrameHint last_flip_hints;
+
   /* Last time we promoted short-term maximum to long-term one */
   int64_t longterm_promotion_us;
   /* Long-term maximum update duration */
@@ -941,11 +943,13 @@ frame_clock_source_dispatch (GSource     *source,
 }
 
 void
-clutter_frame_clock_record_flip_time (ClutterFrameClock *frame_clock,
-                                      int64_t            flip_time_us)
+clutter_frame_clock_record_flip (ClutterFrameClock *frame_clock,
+                                 int64_t            flip_time_us,
+                                 ClutterFrameHint   hints)
 {
   frame_clock->prev_last_flip_time_us = frame_clock->last_flip_time_us;
   frame_clock->last_flip_time_us = flip_time_us;
+  frame_clock->last_flip_hints = hints;
 }
 
 GString *
diff --git a/clutter/clutter/clutter-frame-clock.h b/clutter/clutter/clutter-frame-clock.h
index b6650a5a053..e1fd6b98611 100644
--- a/clutter/clutter/clutter-frame-clock.h
+++ b/clutter/clutter/clutter-frame-clock.h
@@ -97,7 +97,8 @@ void clutter_frame_clock_remove_timeline (ClutterFrameClock *frame_clock,
 CLUTTER_EXPORT
 float clutter_frame_clock_get_refresh_rate (ClutterFrameClock *frame_clock);
 
-void clutter_frame_clock_record_flip_time (ClutterFrameClock *frame_clock,
-                                           int64_t            flip_time_us);
+void clutter_frame_clock_record_flip (ClutterFrameClock *frame_clock,
+                                      int64_t            flip_time_us,
+                                      ClutterFrameHint   hints);
 
 GString * clutter_frame_clock_get_max_render_time_debug_info (ClutterFrameClock *frame_clock);
diff --git a/clutter/clutter/clutter-stage-view.c b/clutter/clutter/clutter-stage-view.c
index 6fab9b87ceb..5669e92d7f9 100644
--- a/clutter/clutter/clutter-stage-view.c
+++ b/clutter/clutter/clutter-stage-view.c
@@ -1265,14 +1265,21 @@ handle_frame_clock_frame (ClutterFrameClock *frame_clock,
 
       _clutter_stage_window_redraw_view (stage_window, view, frame);
 
-      clutter_frame_clock_record_flip_time (frame_clock,
-                                            g_get_monotonic_time ());
+      clutter_frame_clock_record_flip (frame_clock,
+                                       g_get_monotonic_time (),
+                                       clutter_frame_get_hints (frame));
 
       clutter_stage_emit_after_paint (stage, view, frame);
 
       if (_clutter_context_get_show_fps ())
         end_frame_timing_measurement (view);
     }
+  else
+    {
+      clutter_frame_clock_record_flip (frame_clock,
+                                       g_get_monotonic_time (),
+                                       clutter_frame_get_hints (frame));
+    }
 
   _clutter_stage_window_finish_frame (stage_window, view, frame);
 
-- 
GitLab

From 9a35cc18b95a98ce7f817649af8513f224cb0a44 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 7 Sep 2021 19:15:55 +0800
Subject: [PATCH 35/42] clutter/frame-clock: Throttle back to double buffering
 for direct scanout

There's no compositing during direct scanout so the "render" time is zero.
Thus there is no need to implement triple buffering for direct scanouts.
Stick to double buffering and enjoy the lower latency.
---
 clutter/clutter/clutter-frame-clock.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index 1c714f85eb8..f65f31f621f 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -773,6 +773,13 @@ clutter_frame_clock_schedule_update (ClutterFrameClock *frame_clock)
     case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
       return;
     case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
+      if (frame_clock->last_flip_hints & CLUTTER_FRAME_HINT_DIRECT_SCANOUT_ATTEMPTED)
+        {
+          /* Force double buffering, disable triple buffering */
+          frame_clock->pending_reschedule = TRUE;
+          return;
+        }
+
       calculate_next_update_time_us (frame_clock,
                                      &next_update_time_us,
                                      &frame_clock->next_presentation_time_us,
-- 
GitLab

From d0c2f92ebdc8f601e017b47c3c42d3536e459fde Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 10 Mar 2022 16:44:14 +0800
Subject: [PATCH 36/42] clutter/frame-clock: Add environment variable
 MUTTER_DEBUG_TRIPLE_BUFFERING

With possible values {never, auto, always} where auto is the default.

This also allows some unification with automatic throttling for
direct scanout.
---
 clutter/clutter/clutter-frame-clock.c | 53 ++++++++++++++++++++++-----
 1 file changed, 43 insertions(+), 10 deletions(-)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index f65f31f621f..620a25896ce 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -35,6 +35,15 @@ enum
 
 static guint signals[N_SIGNALS];
 
+typedef enum
+{
+  TRIPLE_BUFFERING_MODE_NEVER,
+  TRIPLE_BUFFERING_MODE_AUTO,
+  TRIPLE_BUFFERING_MODE_ALWAYS,
+} TripleBufferingMode;
+
+static TripleBufferingMode triple_buffering_mode = TRIPLE_BUFFERING_MODE_AUTO;
+
 #define SYNC_DELAY_FALLBACK_FRACTION 0.875
 
 typedef struct _ClutterFrameListener
@@ -747,6 +756,12 @@ void
 clutter_frame_clock_schedule_update (ClutterFrameClock *frame_clock)
 {
   int64_t next_update_time_us = -1;
+  TripleBufferingMode current_mode = triple_buffering_mode;
+
+  if (current_mode == TRIPLE_BUFFERING_MODE_AUTO &&
+      (frame_clock->last_flip_hints &
+       CLUTTER_FRAME_HINT_DIRECT_SCANOUT_ATTEMPTED))
+    current_mode = TRIPLE_BUFFERING_MODE_NEVER;
 
   if (frame_clock->inhibit_count > 0)
     {
@@ -773,20 +788,29 @@ clutter_frame_clock_schedule_update (ClutterFrameClock *frame_clock)
     case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED:
       return;
     case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE:
-      if (frame_clock->last_flip_hints & CLUTTER_FRAME_HINT_DIRECT_SCANOUT_ATTEMPTED)
+      switch (current_mode)
         {
-          /* Force double buffering, disable triple buffering */
+        case TRIPLE_BUFFERING_MODE_NEVER:
           frame_clock->pending_reschedule = TRUE;
           return;
+        case TRIPLE_BUFFERING_MODE_AUTO:
+          calculate_next_update_time_us (frame_clock,
+                                         &next_update_time_us,
+                                         &frame_clock->next_presentation_time_us,
+                                         &frame_clock->min_render_time_allowed_us);
+          frame_clock->is_next_presentation_time_valid =
+            (frame_clock->next_presentation_time_us != 0);
+          frame_clock->state =
+            CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED;
+          break;
+        case TRIPLE_BUFFERING_MODE_ALWAYS:
+          next_update_time_us = g_get_monotonic_time ();
+          frame_clock->next_presentation_time_us = 0;
+          frame_clock->is_next_presentation_time_valid = FALSE;
+          frame_clock->state =
+            CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED;
+          break;
         }
-
-      calculate_next_update_time_us (frame_clock,
-                                     &next_update_time_us,
-                                     &frame_clock->next_presentation_time_us,
-                                     &frame_clock->min_render_time_allowed_us);
-      frame_clock->is_next_presentation_time_valid =
-        (frame_clock->next_presentation_time_us != 0);
-      frame_clock->state = CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_ONE_AND_SCHEDULED;
       break;
     case CLUTTER_FRAME_CLOCK_STATE_DISPATCHED_TWO:
       frame_clock->pending_reschedule = TRUE;
@@ -1070,6 +1094,15 @@ static void
 clutter_frame_clock_class_init (ClutterFrameClockClass *klass)
 {
   GObjectClass *object_class = G_OBJECT_CLASS (klass);
+  const char *mode_str;
+
+  mode_str = g_getenv ("MUTTER_DEBUG_TRIPLE_BUFFERING");
+  if (!g_strcmp0 (mode_str, "never"))
+    triple_buffering_mode = TRIPLE_BUFFERING_MODE_NEVER;
+  else if (!g_strcmp0 (mode_str, "auto"))
+    triple_buffering_mode = TRIPLE_BUFFERING_MODE_AUTO;
+  else if (!g_strcmp0 (mode_str, "always"))
+    triple_buffering_mode = TRIPLE_BUFFERING_MODE_ALWAYS;
 
   object_class->dispose = clutter_frame_clock_dispose;
 
-- 
GitLab

From b7c2a22411a3d959a847b762c0457782267ebc6a Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 30 Jun 2022 18:56:06 +0800
Subject: [PATCH 37/42] tests/native-kms-render: Fix failing client-scanout
 test

It was assuming an immediate transition from compositing (triple
buffering) to direct scanout (double buffering), whereas there is
a one frame delay in that transition as the buffer queue shrinks.
We don't lose any frames in the transition.
---
 src/tests/native-kms-render.c | 107 ++++++++++++++++++++++++++++------
 1 file changed, 88 insertions(+), 19 deletions(-)

diff --git a/src/tests/native-kms-render.c b/src/tests/native-kms-render.c
index 8a6a45c5230..b67f3f315c6 100644
--- a/src/tests/native-kms-render.c
+++ b/src/tests/native-kms-render.c
@@ -41,6 +41,8 @@
 #include "tests/meta-wayland-test-driver.h"
 #include "tests/meta-wayland-test-utils.h"
 
+#define N_FRAMES_PER_TEST 30
+
 typedef struct
 {
   int number_of_frames_left;
@@ -48,12 +50,15 @@ typedef struct
 
   struct {
     int n_paints;
-    uint32_t fb_id;
+    int n_presentations;
+    int n_direct_scanouts;
+    GList *fb_ids;
   } scanout;
 
   gboolean wait_for_scanout;
 
   struct {
+    int scanouts_attempted;
     gboolean scanout_sabotaged;
     gboolean fallback_painted;
     guint repaint_guard_id;
@@ -103,7 +108,7 @@ meta_test_kms_render_basic (void)
   gulong handler_id;
 
   test = (KmsRenderingTest) {
-    .number_of_frames_left = 10,
+    .number_of_frames_left = N_FRAMES_PER_TEST,
     .loop = g_main_loop_new (NULL, FALSE),
   };
   handler_id = g_signal_connect (stage, "after-update",
@@ -125,7 +130,6 @@ on_scanout_before_update (ClutterStage     *stage,
                           KmsRenderingTest *test)
 {
   test->scanout.n_paints = 0;
-  test->scanout.fb_id = 0;
 }
 
 static void
@@ -136,6 +140,7 @@ on_scanout_before_paint (ClutterStage     *stage,
 {
   CoglScanout *scanout;
   MetaDrmBuffer *buffer;
+  uint32_t fb_id;
 
   scanout = clutter_stage_view_peek_scanout (stage_view);
   if (!scanout)
@@ -143,8 +148,14 @@ on_scanout_before_paint (ClutterStage     *stage,
 
   g_assert_true (META_IS_DRM_BUFFER (scanout));
   buffer = META_DRM_BUFFER (scanout);
-  test->scanout.fb_id = meta_drm_buffer_get_fb_id (buffer);
-  g_assert_cmpuint (test->scanout.fb_id, >, 0);
+
+  fb_id = meta_drm_buffer_get_fb_id (buffer);
+  g_assert_cmpuint (fb_id, >, 0);
+  test->scanout.fb_ids = g_list_append (test->scanout.fb_ids,
+                                        GUINT_TO_POINTER (fb_id));
+
+  /* Triple buffering, but no higher */
+  g_assert_cmpuint (g_list_length (test->scanout.fb_ids), <=, 2);
 }
 
 static void
@@ -173,12 +184,12 @@ on_scanout_presented (ClutterStage     *stage,
   MetaDeviceFile *device_file;
   GError *error = NULL;
   drmModeCrtc *drm_crtc;
+  uint32_t first_fb_id_expected;
 
-  if (test->wait_for_scanout && test->scanout.n_paints > 0)
+  if (test->wait_for_scanout && test->scanout.fb_ids == NULL)
     return;
 
-  if (test->wait_for_scanout && test->scanout.fb_id == 0)
-    return;
+  test->scanout.n_presentations++;
 
   device_pool = meta_backend_native_get_device_pool (backend_native);
 
@@ -197,15 +208,41 @@ on_scanout_presented (ClutterStage     *stage,
   drm_crtc = drmModeGetCrtc (meta_device_file_get_fd (device_file),
                              meta_kms_crtc_get_id (kms_crtc));
   g_assert_nonnull (drm_crtc);
-  if (test->scanout.fb_id == 0)
-    g_assert_cmpuint (drm_crtc->buffer_id, !=, test->scanout.fb_id);
+
+  if (test->scanout.fb_ids)
+    {
+      test->scanout.n_direct_scanouts++;
+      first_fb_id_expected = GPOINTER_TO_UINT (test->scanout.fb_ids->data);
+      test->scanout.fb_ids = g_list_delete_link (test->scanout.fb_ids,
+                                                 test->scanout.fb_ids);
+    }
   else
-    g_assert_cmpuint (drm_crtc->buffer_id, ==, test->scanout.fb_id);
+    {
+      first_fb_id_expected = 0;
+    }
+
+  /* The buffer ID won't match on the first frame because switching from
+   * triple buffered compositing to double buffered direct scanout takes
+   * an extra frame to drain the queue. Thereafter we are in direct scanout
+   * mode and expect the buffer IDs to match.
+   */
+  if (test->scanout.n_presentations > 1)
+    {
+      if (first_fb_id_expected == 0)
+        g_assert_cmpuint (drm_crtc->buffer_id, !=, first_fb_id_expected);
+      else
+        g_assert_cmpuint (drm_crtc->buffer_id, ==, first_fb_id_expected);
+    }
+
   drmModeFreeCrtc (drm_crtc);
 
   meta_device_file_release (device_file);
 
-  g_main_loop_quit (test->loop);
+  test->number_of_frames_left--;
+  if (test->number_of_frames_left <= 0)
+    g_main_loop_quit (test->loop);
+  else
+    clutter_actor_queue_redraw (CLUTTER_ACTOR (stage));
 }
 
 typedef enum
@@ -244,7 +281,9 @@ meta_test_kms_render_client_scanout (void)
   g_assert_nonnull (wayland_test_client);
 
   test = (KmsRenderingTest) {
+    .number_of_frames_left = N_FRAMES_PER_TEST,
     .loop = g_main_loop_new (NULL, FALSE),
+    .scanout = {0},
     .wait_for_scanout = TRUE,
   };
 
@@ -270,7 +309,8 @@ meta_test_kms_render_client_scanout (void)
   clutter_actor_queue_redraw (CLUTTER_ACTOR (stage));
   g_main_loop_run (test.loop);
 
-  g_assert_cmpuint (test.scanout.fb_id, >, 0);
+  g_assert_cmpint (test.scanout.n_presentations, ==, N_FRAMES_PER_TEST);
+  g_assert_cmpint (test.scanout.n_direct_scanouts, ==, N_FRAMES_PER_TEST);
 
   g_debug ("Unmake fullscreen");
   window = meta_find_window_from_title (test_context, "dma-buf-scanout-test");
@@ -292,10 +332,15 @@ meta_test_kms_render_client_scanout (void)
   g_assert_cmpint (buffer_rect.y, ==, 10);
 
   test.wait_for_scanout = FALSE;
+  test.number_of_frames_left = N_FRAMES_PER_TEST;
+  test.scanout.n_presentations = 0;
+  test.scanout.n_direct_scanouts = 0;
+
   clutter_actor_queue_redraw (CLUTTER_ACTOR (stage));
   g_main_loop_run (test.loop);
 
-  g_assert_cmpuint (test.scanout.fb_id, ==, 0);
+  g_assert_cmpint (test.scanout.n_presentations, ==, N_FRAMES_PER_TEST);
+  g_assert_cmpint (test.scanout.n_direct_scanouts, ==, 0);
 
   g_debug ("Moving back to 0, 0");
   meta_window_move_frame (window, TRUE, 0, 0);
@@ -307,10 +352,15 @@ meta_test_kms_render_client_scanout (void)
   g_assert_cmpint (buffer_rect.y, ==, 0);
 
   test.wait_for_scanout = TRUE;
+  test.number_of_frames_left = N_FRAMES_PER_TEST;
+  test.scanout.n_presentations = 0;
+  test.scanout.n_direct_scanouts = 0;
+
   clutter_actor_queue_redraw (CLUTTER_ACTOR (stage));
   g_main_loop_run (test.loop);
 
-  g_assert_cmpuint (test.scanout.fb_id, >, 0);
+  g_assert_cmpint (test.scanout.n_presentations, ==, N_FRAMES_PER_TEST);
+  g_assert_cmpint (test.scanout.n_direct_scanouts, ==, N_FRAMES_PER_TEST);
 
   g_signal_handler_disconnect (stage, before_update_handler_id);
   g_signal_handler_disconnect (stage, before_paint_handler_id);
@@ -364,6 +414,15 @@ on_scanout_fallback_before_paint (ClutterStage     *stage,
   if (!scanout)
     return;
 
+  test->scanout_fallback.scanouts_attempted++;
+
+  /* The first scanout candidate frame will get composited due to triple
+   * buffering draining the queue to drop to double buffering. So don't
+   * sabotage that first frame.
+   */
+  if (test->scanout_fallback.scanouts_attempted < 2)
+    return;
+
   g_assert_false (test->scanout_fallback.scanout_sabotaged);
 
   if (is_atomic_mode_setting (kms_device))
@@ -401,6 +460,15 @@ on_scanout_fallback_paint_view (ClutterStage     *stage,
       g_clear_handle_id (&test->scanout_fallback.repaint_guard_id,
                          g_source_remove);
       test->scanout_fallback.fallback_painted = TRUE;
+      test->scanout_fallback.scanout_sabotaged = FALSE;
+    }
+  else if (test->scanout_fallback.scanouts_attempted == 1)
+    {
+      /* Now that we've seen the first scanout attempt that was inhibited by
+       * triple buffering, try a second frame. The second one should scanout
+       * and will be sabotaged.
+       */
+      clutter_actor_queue_redraw (CLUTTER_ACTOR (stage));
     }
 }
 
@@ -410,11 +478,11 @@ on_scanout_fallback_presented (ClutterStage     *stage,
                                ClutterFrameInfo *frame_info,
                                KmsRenderingTest *test)
 {
-  if (!test->scanout_fallback.scanout_sabotaged)
-    return;
+  if (test->scanout_fallback.fallback_painted)
+    g_main_loop_quit (test->loop);
 
-  g_assert_true (test->scanout_fallback.fallback_painted);
-  g_main_loop_quit (test->loop);
+  test->number_of_frames_left--;
+  g_assert_cmpint (test->number_of_frames_left, >, 0);
 }
 
 static void
@@ -443,6 +511,7 @@ meta_test_kms_render_client_scanout_fallback (void)
   g_assert_nonnull (wayland_test_client);
 
   test = (KmsRenderingTest) {
+    .number_of_frames_left = N_FRAMES_PER_TEST,
     .loop = g_main_loop_new (NULL, FALSE),
   };
 
-- 
GitLab

From 2eb6fed26df51692d2766e60bbccc272a88eddcf Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 19 May 2023 14:31:07 +0800
Subject: [PATCH 38/42] tests/clutter/event-delivery: Add a wait for
 clutter_actor_destroy

Because the destroy meant we were producing more frames/updates than
were waited on. This becomes a problem when triple buffering is enabled
because stage changes are then delayed by one update, causing spurious
test failures unless we wait on every change to keep it synchronous like
in double buffering.
---
 src/tests/clutter/conform/event-delivery.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/tests/clutter/conform/event-delivery.c b/src/tests/clutter/conform/event-delivery.c
index 383ad0bae08..3b259139a98 100644
--- a/src/tests/clutter/conform/event-delivery.c
+++ b/src/tests/clutter/conform/event-delivery.c
@@ -329,6 +329,7 @@ event_delivery_implicit_grab_cancelled (void)
   n_child_1_leave_events = n_child_2_leave_events = n_stage_leave_events = 0;
   n_action_sequences_cancelled = 0;
   clutter_actor_destroy (child_1);
+  wait_stage_updated (&was_updated);
   g_assert_cmpint (n_child_1_enter_events, ==, 0);
   g_assert_cmpint (n_child_1_leave_events, ==, 0);
   g_assert_cmpint (n_action_sequences_cancelled, ==, 1);
-- 
GitLab

From fde964532645e9d85df700ab8f3826bbc7c0ce0b Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Thu, 22 Jun 2023 15:19:53 +0800
Subject: [PATCH 39/42] onscreen/native: Avoid callbacks on "detached"
 onscreens

Detached onscreens have no valid view so avoid servicing callbacks on
them during/after sleep mode. As previously mentioned in 45bda2d969f.

Fixes: https://launchpad.net/bugs/2020049
---
 src/backends/native/meta-onscreen-native.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 274245bd301..0eb89ec7620 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -1243,7 +1243,8 @@ try_post_latest_swap (CoglOnscreen *onscreen)
   g_autoptr (ClutterFrame) frame = NULL;
   MetaFrameNative *frame_native;
 
-  if (onscreen_native->next_post.frame == NULL)
+  if (onscreen_native->next_post.frame == NULL ||
+      onscreen_native->view == NULL)
     return;
 
   if (meta_kms_is_shutting_down (kms))
-- 
GitLab

From 59227a7f5e76863a549783dc9fab0709d90612ba Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 18 Jul 2023 16:08:25 +0800
Subject: [PATCH 40/42] clutter/frame-clock: Record measurements of zero for
 cursor-only updates

But only if we've ever got actual swap measurements
(COGL_FEATURE_ID_TIMESTAMP_QUERY). If it's supported then we now drop to
double buffering and get optimal latency on a burst of cursor-only
updates.

Fixes: https://launchpad.net/bugs/2023363
---
 clutter/clutter/clutter-frame-clock.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/clutter/clutter/clutter-frame-clock.c b/clutter/clutter/clutter-frame-clock.c
index 620a25896ce..0bb368d8e16 100644
--- a/clutter/clutter/clutter-frame-clock.c
+++ b/clutter/clutter/clutter-frame-clock.c
@@ -233,10 +233,6 @@ static void
 maybe_update_longterm_max_duration_us (ClutterFrameClock *frame_clock,
                                        ClutterFrameInfo  *frame_info)
 {
-  /* Do not update long-term max if there has been no measurement */
-  if (!frame_clock->shortterm_max_update_duration_us)
-    return;
-
   if ((frame_info->presentation_time - frame_clock->longterm_promotion_us) <
       G_USEC_PER_SEC)
     return;
@@ -348,7 +344,8 @@ clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
 
   frame_clock->got_measurements_last_frame = FALSE;
 
-  if (frame_info->cpu_time_before_buffer_swap_us != 0)
+  if (frame_info->cpu_time_before_buffer_swap_us != 0 ||
+      frame_clock->ever_got_measurements)
     {
       int64_t dispatch_to_swap_us, swap_to_rendering_done_us, swap_to_flip_us;
       int64_t dispatch_time_us = 0, flip_time_us = 0;
@@ -371,14 +368,21 @@ clutter_frame_clock_notify_presented (ClutterFrameClock *frame_clock,
           break;
         }
 
-      dispatch_to_swap_us =
-        frame_info->cpu_time_before_buffer_swap_us -
-        dispatch_time_us;
+      if (frame_info->cpu_time_before_buffer_swap_us == 0)
+        {
+          /* Cursor-only updates with no "swap" or "flip" */
+          dispatch_to_swap_us = 0;
+          swap_to_flip_us = 0;
+        }
+      else
+        {
+          dispatch_to_swap_us = frame_info->cpu_time_before_buffer_swap_us -
+                                dispatch_time_us;
+          swap_to_flip_us = flip_time_us -
+                            frame_info->cpu_time_before_buffer_swap_us;
+        }
       swap_to_rendering_done_us =
         frame_info->gpu_rendering_duration_ns / 1000;
-      swap_to_flip_us =
-        flip_time_us -
-        frame_info->cpu_time_before_buffer_swap_us;
 
       CLUTTER_NOTE (FRAME_TIMINGS,
                     "%s: update2dispatch %ld µs, dispatch2swap %ld µs, swap2render %ld µs, swap2flip %ld µs",
-- 
GitLab

From 8f7fe5d151778d72eb5ec958b4d90efd9bc7e2e1 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Wed, 26 Jul 2023 17:27:10 +0800
Subject: [PATCH 41/42] backends/native: Make await_flush much later and
 implicit

Later as in after GL is finished rendering so as to not block the deadline
timer from updating the cursor smoothly during long GL renders.
---
 src/backends/native/meta-kms-impl-device.c | 3 ++-
 src/backends/native/meta-onscreen-native.c | 6 ------
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/src/backends/native/meta-kms-impl-device.c b/src/backends/native/meta-kms-impl-device.c
index 2f9a22a923f..410cf59c87f 100644
--- a/src/backends/native/meta-kms-impl-device.c
+++ b/src/backends/native/meta-kms-impl-device.c
@@ -1485,10 +1485,11 @@ meta_kms_impl_device_handle_update (MetaKmsImplDevice *impl_device,
       meta_kms_update_merge_from (crtc_frame->pending_update, update);
       meta_kms_update_free (update);
       update = g_steal_pointer (&crtc_frame->pending_update);
-      disarm_crtc_frame_deadline_timer (crtc_frame);
     }
 
   meta_kms_device_handle_flush (priv->device, latch_crtc);
+  if (crtc_frame->deadline.armed)
+    disarm_crtc_frame_deadline_timer (crtc_frame);
 
   feedback = do_process (impl_device, latch_crtc, update, flags);
   meta_kms_feedback_unref (feedback);
diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 0eb89ec7620..5d72180b754 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -1555,12 +1555,6 @@ void
 meta_onscreen_native_before_redraw (CoglOnscreen *onscreen,
                                     ClutterFrame *frame)
 {
-  MetaOnscreenNative *onscreen_native = META_ONSCREEN_NATIVE (onscreen);
-  MetaCrtcKms *crtc_kms = META_CRTC_KMS (onscreen_native->crtc);
-  MetaKmsCrtc *kms_crtc = meta_crtc_kms_get_kms_crtc (crtc_kms);
-
-  meta_kms_device_await_flush (meta_kms_crtc_get_device (kms_crtc),
-                               kms_crtc);
 }
 
 void
-- 
GitLab

From 8ecf1337551c6d75706b677bc5e7b00ea18c1191 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 28 Jul 2023 17:24:57 +0800
Subject: [PATCH 42/42] onscreen/native: Tidy up finish_frame and adapt to KMS
 thread

The adaptation is that meta_frame_native_has_kms_update is expected to
always be FALSE now. So this fixes an assertion failure:

onscreen_native->swaps_pending > 0

TODO: Squash this commit once the dust has settled.
---
 src/backends/native/meta-onscreen-native.c | 54 ++++++++++------------
 1 file changed, 25 insertions(+), 29 deletions(-)

diff --git a/src/backends/native/meta-onscreen-native.c b/src/backends/native/meta-onscreen-native.c
index 5d72180b754..b81645a242f 100644
--- a/src/backends/native/meta-onscreen-native.c
+++ b/src/backends/native/meta-onscreen-native.c
@@ -1668,20 +1668,9 @@ meta_onscreen_native_finish_frame (CoglOnscreen *onscreen,
   MetaKmsDevice *kms_device = meta_kms_crtc_get_device (kms_crtc);
   MetaFrameNative *frame_native = meta_frame_native_from_frame (frame);
   MetaKmsUpdate *kms_update;
-
-  if (meta_frame_native_has_kms_update (frame_native) &&
-      cogl_onscreen_count_pending_frames (onscreen) > 0 &&
-      onscreen_native->swaps_pending == 0)
-    {
-      /* Posts are busy AND we have no swaps pending so just retry the same
-       * frame later in try_post_latest_swap.
-       */
-      g_warn_if_fail (onscreen_native->next_post.frame == NULL);
-      g_clear_pointer (&onscreen_native->next_post.frame, clutter_frame_unref);
-      onscreen_native->next_post.frame = clutter_frame_ref (frame);
-      clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
-      return;
-    }
+  unsigned int frames_pending = cogl_onscreen_count_pending_frames (onscreen);
+  unsigned int swaps_pending = onscreen_native->swaps_pending;
+  unsigned int posts_pending = frames_pending - swaps_pending;
 
   kms_update = meta_frame_native_steal_kms_update (frame_native);
   if (!kms_update)
@@ -1698,25 +1687,32 @@ meta_onscreen_native_finish_frame (CoglOnscreen *onscreen,
         }
     }
 
-  if (cogl_onscreen_count_pending_frames (onscreen) > 0)
+  if (posts_pending)
     {
-      /* Posts are busy AND we have swaps pending so best to merge our cursor
-       * update into the pending swap.
-       */
-      MetaFrameNative *older_frame_native;
-      MetaKmsUpdate *older_kms_update;
+      if (!swaps_pending)
+        {
+          g_warn_if_fail (onscreen_native->next_post.frame == NULL);
+          g_clear_pointer (&onscreen_native->next_post.frame, clutter_frame_unref);
+          onscreen_native->next_post.frame = clutter_frame_ref (frame);
+          clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_PENDING_PRESENTED);
+        }
+      else
+        {
+          MetaFrameNative *older_frame_native;
+          MetaKmsUpdate *older_kms_update;
 
-      g_return_if_fail (onscreen_native->swaps_pending > 0);
-      g_return_if_fail (onscreen_native->next_post.frame != NULL);
+          g_assert (swaps_pending);
+          g_return_if_fail (onscreen_native->next_post.frame != NULL);
 
-      older_frame_native =
-        meta_frame_native_from_frame (onscreen_native->next_post.frame);
-      older_kms_update =
-        meta_frame_native_ensure_kms_update (older_frame_native, kms_device);
-      meta_kms_update_merge_from (older_kms_update, kms_update);
-      meta_kms_update_free (kms_update);
+          older_frame_native =
+            meta_frame_native_from_frame (onscreen_native->next_post.frame);
+          older_kms_update =
+            meta_frame_native_ensure_kms_update (older_frame_native, kms_device);
+          meta_kms_update_merge_from (older_kms_update, kms_update);
+          meta_kms_update_free (kms_update);
 
-      clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_IDLE);
+          clutter_frame_set_result (frame, CLUTTER_FRAME_RESULT_IDLE);
+        }
       return;
     }
 
-- 
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File _service:download_url:1441.patch of Package mutter (Revision 6595fc95e300238ccce467441e216c28)

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