[Bug 85367] [gen4] GPU hang in glmark-es2

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=85367

Kenneth Graunke <kenneth at whitecape.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #7 from Kenneth Graunke <kenneth at whitecape.org> ---
I can't find anything indicating what we're doing wrong, but today I committed
a workaround for the problem.  It should be fixed in master with:

commit c4fd0c9052dd391d6f2e9bb8e6da209dfc7ef35b
Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Sat Jan 17 23:21:15 2015 -0800

    i965: Work around mysterious Gen4 GPU hangs with minimal state changes.

    Gen4 hardware appears to GPU hang frequently when using Chromium, and
    also when running 'glmark2 -b ideas'.  Most of the error states contain
    3DPRIMITIVE commands in quick succession, with very few state packets
    between them - usually VERTEX_BUFFERS/ELEMENTS and CONSTANT_BUFFER.

    I trimmed an apitrace of the glmark2 hang down to two draw calls with a
    glUniformMatrix4fv call between the two.  Either draw by itself works
    fine, but together, they hang the GPU.  Removing the glUniform call
    makes the hangs disappear.  In the hardware state, this translates to
    removing the CONSTANT_BUFFER packet between the two 3DPRIMITIVE packets.

    Flushing before emitting CONSTANT_BUFFER packets also appears to make
    the hangs disappear.  I observed a slowdown in glxgears by doing it all
    the time, so I've chosen to only do it when BRW_NEW_BATCH and
    BRW_NEW_PSP are unset (i.e. we haven't done a CS_URB_STATE change or
    already flushed the whole pipeline).

    I'd much rather understand the problem, but at this point, I don't see
    how we'd ever be able to track it down further.  We have no real tools,
    and the hardware people moved on years ago.  I've analyzed 20+ error
    states and read every scrap of documentation I could find.

    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=80568
    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85367
    Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
    Acked-by: Matt Turner <mattst88 at gmail.com>
    Cc: "10.4 10.3" <mesa-stable at lists.freedesktop.org>

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