File libxl.add-option-to-disable-disk-cache-flushes-... of Package xen

Overview Repositories Revisions Requests Users Attributes Meta

File libxl.add-option-to-disable-disk-cache-flushes-in-qdisk.patch of Package xen (Revision 74de522d745c4511f01911427a77a8e0)

Currently displaying revision 74de522d745c4511f01911427a77a8e0 , Show latest

https://bugzilla.novell.com/show_bug.cgi?id=879425
---
 tools/libxl/libxl.c         |    2 ++
 tools/libxl/libxl.h         |   12 ++++++++++++
 tools/libxl/libxlu_disk.c   |    2 ++
 tools/libxl/libxlu_disk_i.h |    2 +-
 tools/libxl/libxlu_disk_l.l |    1 +
 5 files changed, 18 insertions(+), 1 deletion(-)

--- a/docs/man/xl-disk-configuration.5.pod
+++ b/docs/man/xl-disk-configuration.5.pod
@@ -344,6 +344,32 @@ can be used to disable "hole punching" f
 were intentionally created non-sparse to avoid fragmentation of the
 file.
 
+=item B<suse-diskcache-disable-flush>
+
+=over 4
+
+=item Description
+
+Request that the qemu block driver does not automatically flush written data to the backend storage.
+
+=item Supported values
+
+absent, present
+
+=item Mandatory
+
+No
+
+=item Default value
+
+absent
+
+=back
+
+This enables the '-disk cache=unsafe' mode inside qemu.
+In this mode writes to the underlying blockdevice are delayed.
+While using this option in production is dangerous, it improves performance during installation of a domU.
+
 =back
 
 
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -386,6 +386,21 @@
 #define LIBXL_HAVE_EXTENDED_VKB 1
 
 /*
+ * The libxl_device_disk has no way to indicate that cache=unsafe is
+ * supposed to be used. Provide this knob without breaking the ABI.
+ * This is done by overloading struct libxl_device_disk->readwrite:
+ * readwrite == 0: disk is readonly, cache= does not matter
+ * readwrite == 1: disk is readwrite, backend driver may tweak cache=
+ * readwrite == MAGIC: disk is readwrite, backend driver should ignore
+ * flush requests from the frontend driver.
+ * Note: the macro with MAGIC is used by libvirt to decide if this patch is applied
+ */
+#define LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MAGIC 0x00006000U
+#define LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MASK  0xffff0fffU
+#define LIBXL_SUSE_IS_CACHE_UNSAFE(rw) (((rw) & ~LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MASK) == LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MAGIC)
+#define LIBXL_SUSE_SET_CACHE_UNSAFE(rw) (((rw) & LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MASK) | LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MAGIC)
+
+/*
  * libxl ABI compatibility
  *
  * The only guarantee which libxl makes regarding ABI compatibility
--- a/tools/libxl/libxl_disk.c
+++ b/tools/libxl/libxl_disk.c
@@ -405,6 +405,8 @@ static void device_disk_add(libxl__egc *
         flexarray_append_pair(back, "discard-enable",
                               libxl_defbool_val(disk->discard_enable) ?
                               "1" : "0");
+        if (LIBXL_SUSE_IS_CACHE_UNSAFE(disk->readwrite))
+            flexarray_append_pair(back, "suse-diskcache-disable-flush", "1");
 
         flexarray_append(front, "backend-id");
         flexarray_append(front, GCSPRINTF("%d", disk->backend_domid));
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -984,14 +984,27 @@ enum {
     LIBXL__COLO_SECONDARY,
 };
 
+static const char *qemu_cache_mode(const libxl_device_disk *disk)
+{
+    static const char cache_directsync[] = "directsync";
+    static const char cache_writeback[] = "writeback";
+    static const char cache_unsafe[] = "unsafe";
+
+    if (LIBXL_SUSE_IS_CACHE_UNSAFE(disk->readwrite))
+        return cache_unsafe;
+    if (disk->direct_io_safe)
+        return cache_directsync;
+    return cache_writeback;
+}
+
 static char *qemu_disk_scsi_drive_string(libxl__gc *gc, const char *target_path,
                                          int unit, const char *format,
                                          const libxl_device_disk *disk,
                                          int colo_mode, const char **id_ptr)
 {
     char *drive = NULL;
-    char *common = GCSPRINTF("if=none,readonly=%s,cache=writeback",
-                             disk->readwrite ? "off" : "on");
+    char *common = GCSPRINTF("if=none,readonly=%s,cache=%s",
+                             disk->readwrite ? "off" : "on", qemu_cache_mode(disk));
     const char *exportname = disk->colo_export;
     const char *active_disk = disk->active_disk;
     const char *hidden_disk = disk->hidden_disk;
@@ -1050,8 +1063,8 @@ static char *qemu_disk_ide_drive_string(
     switch (colo_mode) {
     case LIBXL__COLO_NONE:
         drive = GCSPRINTF
-            ("file=%s,if=ide,index=%d,media=disk,format=%s,cache=writeback",
-             target_path, unit, format);
+            ("file=%s,if=ide,index=%d,media=disk,format=%s,cache=%s",
+             target_path, unit, format, qemu_cache_mode(disk));
         break;
     case LIBXL__COLO_PRIMARY:
         /*
@@ -1064,13 +1077,14 @@ static char *qemu_disk_ide_drive_string(
          *  vote-threshold=1
          */
         drive = GCSPRINTF(
-            "if=ide,index=%d,media=disk,cache=writeback,driver=quorum,"
+            "if=ide,index=%d,media=disk,cache=%s,driver=quorum,"
             "id=%s,"
             "children.0.file.filename=%s,"
             "children.0.driver=%s,"
             "read-pattern=fifo,"
             "vote-threshold=1",
-             unit, exportname, target_path, format);
+            unit, qemu_cache_mode(disk),
+            exportname, target_path, format);
         break;
     case LIBXL__COLO_SECONDARY:
         /*
@@ -1084,7 +1098,7 @@ static char *qemu_disk_ide_drive_string(
          *  file.backing.backing=exportname,
          */
         drive = GCSPRINTF(
-            "if=ide,index=%d,id=top-colo,media=disk,cache=writeback,"
+            "if=ide,index=%d,id=top-colo,media=disk,cache=%s,"
             "driver=replication,"
             "mode=secondary,"
             "top-id=top-colo,"
@@ -1093,7 +1107,8 @@ static char *qemu_disk_ide_drive_string(
             "file.backing.driver=qcow2,"
             "file.backing.file.filename=%s,"
             "file.backing.backing=%s",
-            unit, active_disk, hidden_disk, exportname);
+            unit, qemu_cache_mode(disk),
+            active_disk, hidden_disk, exportname);
         break;
     default:
          abort();
@@ -1890,8 +1905,8 @@ static int libxl__build_device_model_arg
                         return ERROR_INVAL;
                     }
                     flexarray_vappend(dm_args, "-drive",
-                        GCSPRINTF("file=%s,if=none,id=ahcidisk-%d,format=%s,cache=writeback",
-                        target_path, disk, format),
+                        GCSPRINTF("file=%s,if=none,id=ahcidisk-%d,format=%s,cache=%s",
+                        target_path, disk, format, qemu_cache_mode(&disks[i])),
                         "-device", GCSPRINTF("ide-hd,bus=ahci0.%d,unit=0,drive=ahcidisk-%d",
                         disk, disk), NULL);
                     continue;
--- a/tools/libxl/libxlu_disk.c
+++ b/tools/libxl/libxlu_disk.c
@@ -79,6 +79,8 @@ int xlu_disk_parse(XLU_Config *cfg,
         if (!disk->pdev_path || !strcmp(disk->pdev_path, ""))
             disk->format = LIBXL_DISK_FORMAT_EMPTY;
     }
+    if (disk->readwrite && dpc.suse_diskcache_disable_flush)
+        disk->readwrite = LIBXL_SUSE_SET_CACHE_UNSAFE(disk->readwrite);
 
     if (!disk->vdev) {
         xlu__disk_err(&dpc,0, "no vdev specified");
--- a/tools/libxl/libxlu_disk_i.h
+++ b/tools/libxl/libxlu_disk_i.h
@@ -10,7 +10,7 @@ typedef struct {
     void *scanner;
     YY_BUFFER_STATE buf;
     libxl_device_disk *disk;
-    int access_set, had_depr_prefix;
+    int access_set, suse_diskcache_disable_flush, had_depr_prefix;
     const char *spec;
 } DiskParseContext;
 
--- a/tools/libxl/libxlu_disk_l.l
+++ b/tools/libxl/libxlu_disk_l.l
@@ -196,6 +196,7 @@ colo-port=[^,]*,?	{ STRIP(','); setcolop
 colo-export=[^,]*,?	{ STRIP(','); SAVESTRING("colo-export", colo_export, FROMEQUALS); }
 active-disk=[^,]*,?	{ STRIP(','); SAVESTRING("active-disk", active_disk, FROMEQUALS); }
 hidden-disk=[^,]*,?	{ STRIP(','); SAVESTRING("hidden-disk", hidden_disk, FROMEQUALS); }
+suse-diskcache-disable-flush,? { DPC->suse_diskcache_disable_flush = 1; }
 
  /* the target magic parameter, eats the rest of the string */

Places

File libxl.add-option-to-disable-disk-cache-flushes-in-qdisk.patch of Package xen (Revision 74de522d745c4511f01911427a77a8e0)

Places