[Bug 108888] [CI][SHARDS] igt at gem_exec_fence@basic-await-default - fail - Failed assertion: out[n] == 0
bugzilla-daemon at freedesktop.org
bugzilla-daemon at freedesktop.org
Mon Dec 31 10:00:36 UTC 2018
https://bugs.freedesktop.org/show_bug.cgi?id=108888
--- Comment #5 from Martin Peres <martin.peres at free.fr> ---
(In reply to Chris Wilson from comment #3)
> Haswell is no longer the odd one out,
>
> commit 6faf5916e6beb0dedb0fcbbafbaa152adeaea758
> Author: Chris Wilson <chris at chris-wilson.co.uk>
> Date: Fri Dec 28 14:07:35 2018 +0000
>
> drm/i915: Remove HW semaphores for gen7 inter-engine synchronisation
>
> The writing is on the wall for the existence of a single execution queue
> along each engine, and as a consequence we will not be able to track
> dependencies along the HW queue itself, i.e. we will not be able to use
> HW semaphores on gen7 as they use a global set of registers (and unlike
> gen8+ we can not effectively target memory to keep per-context seqno and
> dependencies).
>
> On the positive side, when we implement request reordering for gen7 we
> also can not presume a simple execution queue and would also require
> removing the current semaphore generation code. So this bring us another
> step closer to request reordering for ringbuffer submission!
>
> The negative side is that using interrupts to drive inter-engine
> synchronisation is much slower (4us -> 15us to do a nop on each of the 3
> engines on ivb). This is much better than it was at the time of
> introducing
> the HW semaphores and equally important userspace weaned itself off
> intermixing dependent BLT/RENDER operations (the prime culprit was glyph
> rendering in UXA). So while we regress the microbenchmarks, it should not
> impact the user.
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=108888
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Link:
> https://patchwork.freedesktop.org/patch/msgid/20181228140736.32606-2-
> chris at chris-wilson.co.uk
Thanks! Let's hope it fixes the IVB and BYT issues too (which are also gen7).
So far, it's been only 2 drmtip runs since this patch landed but the
reproduction rate was quite sporadic, so I guess we'll have to be a little
patient.
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