File 0001-net-drivers-ieee1275-ofnet-Remove-200-ms-t... of Package grub2

Overview Repositories Revisions Requests Users Attributes Meta

File 0001-net-drivers-ieee1275-ofnet-Remove-200-ms-timeout-in-.patch of Package grub2 (Revision a8fad39ff8d8779f5239ecfea230b2f2)

Currently displaying revision a8fad39ff8d8779f5239ecfea230b2f2 , Show latest

From d35ff22516b161f6d472f7f5371a89597b072d04 Mon Sep 17 00:00:00 2001
From: Michael Chang <mchang@suse.com>
Date: Mon, 6 May 2024 10:34:22 +0800
Subject: [PATCH] net/drivers/ieee1275/ofnet: Remove 200 ms timeout in
 get_card_packet() to reduce input latency

When GRUB image is netbooted on ppc64le, the keyboard input exhibits
significant latency, reports even say that characters are processed
about once per second. This issue makes interactively trying to debug
a ppc64le config very difficult.

It seems that the latency is largely caused by a 200 ms timeout in the
idle event loop, during which the network card interface is consistently
polled for incoming packets. Often, no packets arrive during this
period, so the timeout nearly always expires, which blocks the response
to key inputs.

Furthermore, this 200 ms timeout might not need to be enforced at this
basic layer, considering that GRUB performs synchronous reads and its
timeout management is actually handled by higher layers, not directly in
the card instance. Additionally, the idle polling, which reacts to
unsolicited packets like ICMP and SLAAC, would be fine at a less frequent
polling interval, rather than needing a timeout for receiving a response.

For these reasons, we believe the timeout in get_card_packet() should be
effectively removed. According to test results, the delay has disappeared,
and it is now much easier to use interactively.

Signed-Off-by: Michael Chang <mchang@suse.com>
Tested-by: Tony Jones <tonyj@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/net/drivers/ieee1275/ofnet.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/grub-core/net/drivers/ieee1275/ofnet.c b/grub-core/net/drivers/ieee1275/ofnet.c
index 78f03df8e..3bf48b3f0 100644
--- a/grub-core/net/drivers/ieee1275/ofnet.c
+++ b/grub-core/net/drivers/ieee1275/ofnet.c
@@ -82,15 +82,11 @@ get_card_packet (struct grub_net_card *dev)
   grub_ssize_t actual;
   int rc;
   struct grub_ofnetcard_data *data = dev->data;
-  grub_uint64_t start_time;
   struct grub_net_buff *nb;
 
-  start_time = grub_get_time_ms ();
-  do
-    rc = grub_ieee1275_read (data->handle, dev->rcvbuf, dev->rcvbufsize, &actual);
-  while ((actual <= 0 || rc < 0) && (grub_get_time_ms () - start_time < 200));
+  rc = grub_ieee1275_read (data->handle, dev->rcvbuf, dev->rcvbufsize, &actual);
 
-  if (actual <= 0)
+  if (actual <= 0 || rc < 0)
     return NULL;
 
   nb = grub_netbuff_alloc (actual + 2);
-- 
2.45.2

Places

File 0001-net-drivers-ieee1275-ofnet-Remove-200-ms-timeout-in-.patch of Package grub2 (Revision a8fad39ff8d8779f5239ecfea230b2f2)

Places