[Bug 95372] [BAT BYT] Sporadic failure from igt/gem_exec_flush at basic-batch-kernel-default-cmd

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=95372

Chris Wilson <chris at chris-wilson.co.uk> changed:

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

--- Comment #8 from Chris Wilson <chris at chris-wilson.co.uk> ---

commit 3b5724d702ef24ee41ca008a1fab1cf94f3d31b5
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Thu Aug 18 17:16:49 2016 +0100

    drm/i915: Wait for writes through the GTT to land before reading back

    If we quickly switch from writing through the GTT to a read of the
    physical page directly with the CPU (e.g. performing relocations through
    the GTT and then running the command parser), we can observe that the
    writes are not visible to the CPU. It is not a coherency problem, as
    extensive investigations with clflush have demonstrated, but a mere
    timing issue - we have to wait for the GTT to complete it's write before
    we start our read from the CPU.

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