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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - [GEN9] 20% perf drop in windowed/composited GpuTest Triangle"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108598#c10">Comment # 10</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - [GEN9] 20% perf drop in windowed/composited GpuTest Triangle"
href="https://bugs.freedesktop.org/show_bug.cgi?id=108598">bug 108598</a>
from <span class="vcard"><a class="email" href="mailto:chris@chris-wilson.co.uk" title="Chris Wilson <chris@chris-wilson.co.uk>"> <span class="fn">Chris Wilson</span></a>
</span></b>
<pre>(In reply to Chris Wilson from <a href="show_bug.cgi?id=108598#c9">comment #9</a>)
<span class="quote">> Had a stable 2% drop on bxt. The effect was due to reordering the requests
> to make i915_spin_request() more likely to be taken. The cost was not from
> reordering the requests themselves, but the act of busywaiting.
>
> i.e.
>
> diff --git a/drivers/gpu/drm/i915/i915_request.c
> b/drivers/gpu/drm/i915/i915_request.c
> index abd4dacbab8e..f5d4659a4aa0 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -1230,6 +1230,11 @@ long i915_request_wait(struct i915_request *rq,
> if (!timeout)
> return -ETIME;
>
> + /* Optimistic short spin before touching IRQs */
> + wait.seqno = i915_request_global_seqno(rq);
> + if (wait.seqno && __i915_spin_request(rq, wait.seqno, state, 5))
> + return timeout;
> +
> trace_i915_request_wait_begin(rq, flags);
>
> add_wait_queue(&rq->execute, &exec);
> @@ -1266,10 +1271,6 @@ long i915_request_wait(struct i915_request *rq,
> GEM_BUG_ON(!intel_wait_has_seqno(&wait));
> GEM_BUG_ON(!i915_sw_fence_signaled(&rq->submit));
>
> - /* Optimistic short spin before touching IRQs */
> - if (__i915_spin_request(rq, wait.seqno, state, 5))
> - goto complete;
> -</span >
Fwiw, this made it into
commit 52c0fdb25c7c919334b97976d05096b441a3eada
Author: Chris Wilson <<a href="mailto:chris@chris-wilson.co.uk">chris@chris-wilson.co.uk</a>>
Date: Tue Jan 29 20:52:29 2019 +0000
drm/i915: Replace global breadcrumbs with per-context interrupt tracking
So that should be my small reproducer fixed, but the larger drop is still a
mystery.</pre>
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