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drm/i915: Prioritise non-busywait semaphore workloads

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We don't want to busywait on the GPU if we have other work to do. If we
give non-busywaiting workloads higher (initial) priority than workloads
that require a busywait, we will prioritise work that is ready to run
immediately. We then also have to be careful that we don't give earlier
semaphores an accidental boost because later work doesn't wait on other
rings, hence we keep a history of semaphore usage of the dependency chain.

v2: Stop rolling the bits into a chain and just use a flag in case this
request or any of our dependencies use a semaphore. The rolling around
was contagious as Tvrtko was heard to fall off his chair.

Testcase: igt/gem_exec_schedule/semaphore
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190301170901.8340-4-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson
2019-03-01 17:09:01 +00:00
parent e886196469
commit f9e9e9de58
4 changed files with 29 additions and 4 deletions
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16
drivers/gpu/drm/i915/i915_request.c
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@@ -813,6 +813,7 @@ emit_semaphore_wait(struct i915_request *to,
*cs++ = 0;
intel_ring_advance(to, cs);
to->sched.flags |= I915_SCHED_HAS_SEMAPHORE;
return 0;
}
@@ -1083,6 +1084,21 @@ void i915_request_add(struct i915_request *request)
if (engine->schedule) {
struct i915_sched_attr attr = request->gem_context->sched;
/*
* Boost actual workloads past semaphores!
*
* With semaphores we spin on one engine waiting for another,
* simply to reduce the latency of starting our work when
* the signaler completes. However, if there is any other
* work that we could be doing on this engine instead, that
* is better utilisation and will reduce the overall duration
* of the current work. To avoid PI boosting a semaphore
* far in the distance past over useful work, we keep a history
* of any semaphore use along our dependency chain.
*/
if (!(request->sched.flags & I915_SCHED_HAS_SEMAPHORE))
attr.priority |= I915_PRIORITY_NOSEMAPHORE;
/*
* Boost priorities to new clients (new request flows).
*