drm/i915: Deconstruct execute fence

On reflection, we are only using the execute fence as a waitqueue on the
global_seqno and not using it for dependency tracking between fences
(unlike the submit and dma fences). By only treating it as a waitqueue,
we can then treat it similar to the other waitqueues during submit,
making the code simpler.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170223074422.4125-8-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_request.c

@@ -69,7 +69,6 @@ static void i915_fence_release(struct dma_fence *fence)
 	 * caught trying to reuse dead objects.
 	 */
 	i915_sw_fence_fini(&req->submit);
-	i915_sw_fence_fini(&req->execute);
 
 	kmem_cache_free(req->i915->requests, req);
 }
@@ -294,7 +293,6 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 
 	lockdep_assert_held(&request->i915->drm.struct_mutex);
 	GEM_BUG_ON(!i915_sw_fence_signaled(&request->submit));
-	GEM_BUG_ON(!i915_sw_fence_signaled(&request->execute));
 	GEM_BUG_ON(!i915_gem_request_completed(request));
 	GEM_BUG_ON(!request->i915->gt.active_requests);
 
@@ -402,6 +400,8 @@ void __i915_gem_request_submit(struct drm_i915_gem_request *request)
 	struct intel_timeline *timeline;
 	u32 seqno;
 
+	trace_i915_gem_request_execute(request);
+
 	/* Transfer from per-context onto the global per-engine timeline */
 	timeline = engine->timeline;
 	GEM_BUG_ON(timeline == request->timeline);
@@ -426,8 +426,7 @@ void __i915_gem_request_submit(struct drm_i915_gem_request *request)
 	list_move_tail(&request->link, &timeline->requests);
 	spin_unlock(&request->timeline->lock);
 
-	i915_sw_fence_commit(&request->execute);
-	trace_i915_gem_request_execute(request);
+	wake_up_all(&request->execute);
 }
 
 void i915_gem_request_submit(struct drm_i915_gem_request *request)
@@ -463,24 +462,6 @@ submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
 	return NOTIFY_DONE;
 }
 
-static int __i915_sw_fence_call
-execute_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
-{
-	struct drm_i915_gem_request *request =
-		container_of(fence, typeof(*request), execute);
-
-	switch (state) {
-	case FENCE_COMPLETE:
-		break;
-
-	case FENCE_FREE:
-		i915_gem_request_put(request);
-		break;
-	}
-
-	return NOTIFY_DONE;
-}
-
 /**
  * i915_gem_request_alloc - allocate a request structure
  *
@@ -573,13 +554,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 
 	/* We bump the ref for the fence chain */
 	i915_sw_fence_init(&i915_gem_request_get(req)->submit, submit_notify);
-	i915_sw_fence_init(&i915_gem_request_get(req)->execute, execute_notify);
-
-	/* Ensure that the execute fence completes after the submit fence -
-	 * as we complete the execute fence from within the submit fence
-	 * callback, its completion would otherwise be visible first.
-	 */
-	i915_sw_fence_await_sw_fence(&req->execute, &req->submit, &req->execq);
+	init_waitqueue_head(&req->execute);
 
 	i915_priotree_init(&req->priotree);
 
@@ -1031,6 +1006,7 @@ long i915_wait_request(struct drm_i915_gem_request *req,
 		TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
 	wait_queue_head_t *errq = &req->i915->gpu_error.wait_queue;
 	DEFINE_WAIT(reset);
+	DEFINE_WAIT(exec);
 	struct intel_wait wait;
 
 	might_sleep();
@@ -1052,12 +1028,11 @@ long i915_wait_request(struct drm_i915_gem_request *req,
 	if (flags & I915_WAIT_LOCKED)
 		add_wait_queue(errq, &reset);
 
-	if (!i915_sw_fence_done(&req->execute)) {
-		DEFINE_WAIT(exec);
-
+	reset_wait_queue(&req->execute, &exec);
+	if (!req->global_seqno) {
 		do {
-			prepare_to_wait(&req->execute.wait, &exec, state);
-			if (i915_sw_fence_done(&req->execute))
+			set_current_state(state);
+			if (req->global_seqno)
 				break;
 
 			if (flags & I915_WAIT_LOCKED &&
@@ -1080,15 +1055,14 @@ long i915_wait_request(struct drm_i915_gem_request *req,
 
 			timeout = io_schedule_timeout(timeout);
 		} while (1);
-		finish_wait(&req->execute.wait, &exec);
+		finish_wait(&req->execute, &exec);
 
 		if (timeout < 0)
 			goto complete;
 
-		GEM_BUG_ON(!i915_sw_fence_done(&req->execute));
-	}
-	GEM_BUG_ON(!i915_sw_fence_done(&req->submit));
 		GEM_BUG_ON(!req->global_seqno);
+	}
+	GEM_BUG_ON(!i915_sw_fence_signaled(&req->submit));
 
 	/* Optimistic short spin before touching IRQs */
 	if (i915_spin_request(req, state, 5))

drivers/gpu/drm/i915/i915_gem_request.h

@@ -119,18 +119,10 @@ struct drm_i915_gem_request {
 	 * The submit fence is used to await upon all of the request's
 	 * dependencies. When it is signaled, the request is ready to run.
 	 * It is used by the driver to then queue the request for execution.
-	 *
-	 * The execute fence is used to signal when the request has been
-	 * sent to hardware.
-	 *
-	 * It is illegal for the submit fence of one request to wait upon the
-	 * execute fence of an earlier request. It should be sufficient to
-	 * wait upon the submit fence of the earlier request.
 	 */
 	struct i915_sw_fence submit;
-	struct i915_sw_fence execute;
 	wait_queue_t submitq;
-	wait_queue_t execq;
+	wait_queue_head_t execute;
 
 	/* A list of everyone we wait upon, and everyone who waits upon us.
 	 * Even though we will not be submitted to the hardware before the