[Bug 108656] [CI][BAT bsw] igt at gem_* - fail - Failed assertion: !"GPU hung"

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108656

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

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

--- Comment #22 from Chris Wilson <chris at chris-wilson.co.uk> ---
A new hope:

commit 8cd999181f8c744c87fb64e7b3600876ec3428b2
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Mon Jan 14 21:17:27 2019 +0000

    drm/i915: Prevent concurrent GGTT update and use on Braswell (again)

    On Braswell, under heavy stress, if we update the GGTT while
    simultaneously accessing another region inside the GTT, we are returned
    the wrong values. To prevent this we stop the machine to update the GGTT
    entries so that no memory traffic can occur at the same time.

    This was first spotted in

    commit 5bab6f60cb4d1417ad7c599166bcfec87529c1a2
    Author: Chris Wilson <chris at chris-wilson.co.uk>
    Date:   Fri Oct 23 18:43:32 2015 +0100

        drm/i915: Serialise updates to GGTT with access through GGTT on
Braswell

    but removed again in forlorn hope with

    commit 4509276ee824bb967885c095c610767e42345c36
    Author: Chris Wilson <chris at chris-wilson.co.uk>
    Date:   Mon Feb 20 12:47:18 2017 +0000

        drm/i915: Remove Braswell GGTT update w/a

    However, gem_concurrent_blit is once again only stable with the patch
    applied and CI is detecting the odd failure in forked gem_mmap_gtt tests
    (which smell like the same issue). Fwiw, a wide variety of CPU memory
    barriers (around GGTT flushing, fence updates, PTE updates) and GPU
    flushes/invalidates (between requests, after PTE updates) were tried as
    part of the investigation to find an alternate cause, nothing comes
    close to serialised GGTT updates.

    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105591
    Testcase: igt/gem_concurrent_blit
    Testcase: igt/gem_mmap_gtt/*forked*
    References: 5bab6f60cb4d ("drm/i915: Serialise updates to GGTT with access
through GGTT on Braswell")
    References: 4509276ee824 ("drm/i915: Remove Braswell GGTT update w/a")
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
    Link:
https://patchwork.freedesktop.org/patch/msgid/20190114211729.30352-1-chris@chris-wilson.co.uk

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