Commit 3f6a6f34 authored by Chris Wilson's avatar Chris Wilson Committed by Joonas Lahtinen
Browse files

drm/i915: Reduce i915_request.lock contention for i915_request_wait 



Currently, we use i915_request_completed() directly in
i915_request_wait() and follow up with a manual invocation of
dma_fence_signal(). This appears to cause a large number of contentions
on i915_request.lock as when the process is woken up after the fence is
signaled by an interrupt, we will then try and call dma_fence_signal()
ourselves while the signaler is still holding the lock.
dma_fence_is_signaled() has the benefit of checking the
DMA_FENCE_FLAG_SIGNALED_BIT prior to calling dma_fence_signal() and so
avoids most of that contention.

Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200716100754.5670-1-chris@chris-wilson.co.uk


Signed-off-by: default avatarRodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: default avatarJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
parent 33936499

drivers/gpu/drm/i915/i915_request.c

+8 −10
Original line number Diff line number Diff line
@@ -1640,7 +1640,7 @@ static bool busywait_stop(unsigned long timeout, unsigned int cpu) 
	return this_cpu != cpu;

}



static bool __i915_spin_request(const struct i915_request * const rq, int state)

static bool __i915_spin_request(struct i915_request * const rq, int state)

{

	unsigned long timeout_ns;

	unsigned int cpu;
@@ -1673,7 +1673,7 @@ static bool __i915_spin_request(const struct i915_request * const rq, int state) 
	timeout_ns = READ_ONCE(rq->engine->props.max_busywait_duration_ns);

	timeout_ns += local_clock_ns(&cpu);

	do {

		if (i915_request_completed(rq))

		if (dma_fence_is_signaled(&rq->fence))

			return true;



		if (signal_pending_state(state, current))
@@ -1697,7 +1697,7 @@ static void request_wait_wake(struct dma_fence *fence, struct dma_fence_cb *cb) 
{

	struct request_wait *wait = container_of(cb, typeof(*wait), cb);



	wake_up_process(wait->tsk);

	wake_up_process(fetch_and_zero(&wait->tsk));

}



/**
@@ -1766,10 +1766,8 @@ long i915_request_wait(struct i915_request *rq, 
	 * duration, which we currently lack.

	 */

	if (IS_ACTIVE(CONFIG_DRM_I915_MAX_REQUEST_BUSYWAIT) &&

	    __i915_spin_request(rq, state)) {

		dma_fence_signal(&rq->fence);

	    __i915_spin_request(rq, state))

		goto out;

	}



	/*

	 * This client is about to stall waiting for the GPU. In many cases
@@ -1793,10 +1791,8 @@ long i915_request_wait(struct i915_request *rq, 
	for (;;) {

		set_current_state(state);



		if (i915_request_completed(rq)) {

			dma_fence_signal(&rq->fence);

		if (dma_fence_is_signaled(&rq->fence))

			break;

		}



		intel_engine_flush_submission(rq->engine);
@@ -1814,7 +1810,9 @@ long i915_request_wait(struct i915_request *rq, 
	}

	__set_current_state(TASK_RUNNING);



	if (READ_ONCE(wait.tsk))

		dma_fence_remove_callback(&rq->fence, &wait.cb);

	GEM_BUG_ON(!list_empty(&wait.cb.node));



out:

	mutex_release(&rq->engine->gt->reset.mutex.dep_map, _THIS_IP_);