On Tue, 2011-06-21 at 11:38 -0400, Robert Hooker wrote:
> Please consider pulling the following change into natty to fix LP #761065.
> SRU Justification:
> Fixes a constant stream of hangcheck errors flooding dmesg, and
> removes the visible stuttering that was caused by it when using 3D
> Fixes missed interrupts on sandybridge GPU's. It doesn't affect any
> other GPU generation.
> Upstream commit 498e720b96379d8ee9c294950a01534a73defcf3.
> 1) Install mesa-utils on a system using sandybridge graphics on 11.04
> 2) run vblank_mode=0 glxgears and let it run for 30 seconds or so
> 3) kill it then check dmesg
> 4) Without fix: hangcheck messages every ~5 seconds, massive
> stuttering of the whole desktop observed. With fix: no hangcheck
> messages, able to continue using the desktop.
Don't forget to add the above SRU Justification, Impact, and Testcase to
the bug description for the SRU Team.
> This was sent to stable, but 2.6.38.y stable is dead so it will need
> to be manually cherry-picked. It has been tested extensively locally
> as well as by users on the bug whom I provided test kernels for. It
> applies cleanly to ubuntu-natty.git.
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=498e720b96379d8ee9c294950a01534 a73defcf3
> drm/i915: Fix gen6 (SNB) missed BLT ring interrupts.
> The failure appeared in dmesg as:
> [drm:i915_hangcheck_ring_idle] *ERROR* Hangcheck timer elapsed... blt
> ring idle [waiting on 35064155, at 35064155], missed IRQ?
> This works around that problem on by making the blitter command
> streamer write interrupt state to the Hardware Status Page when a
> MI_USER_INTERRUPT command is decoded, which appears to force the seqno
> out to memory before the interrupt happens.
> v1->v2: Moved to prior interrupt handler installation and RMW flags as
> per feedback.
> v2->v3: Removed RMW of flags (by anholt)
> Cc: email@example.com
> Signed-off-by: Daniel J Blueman <firstname.lastname@example.org>
> Signed-off-by: Eric Anholt <email@example.com>
> Tested-by: Chris Wilson <firstname.lastname@example.org> [v1]
> Tested-by: Eric Anholt <email@example.com> [v1,v3]
> (incidence of the bug with a testcase went from avg 2/1000 to
> 0/12651 in the latest test run (plus more for v1))
> Tested-by: Kenneth Graunke <firstname.lastname@example.org> [v1]
> Tested-by: Robert Hooker <email@example.com> [v1]
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=33394
> Signed-off-by: Dave Airlie <firstname.lastname@example.org>
Looks reasonable for Natty SRU with minimal risk of regression and has
positive test results.