drm/i915: Defer transfer onto execution timeline to actual hw submission

Defer the transfer from the client's timeline onto the execution
timeline from the point of readiness to the point of actual submission.
For example, in execlists, a request is finally submitted to hardware
when the hardware is ready, and only put onto the hardware queue when
the request is ready. By deferring the transfer, we ensure that the
timeline is maintained in retirement order if we decide to queue the
requests onto the hardware in a different order than fifo.

v2: Rebased onto distinct global/user timeline lock classes.
v3: Play with the position of the spin_lock().
v4: Nesting finally resolved with distinct sw_fence lock classes.

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/20161114204105.29171-4-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_request.c

@@ -306,25 +306,16 @@ static u32 timeline_get_seqno(struct i915_gem_timeline *tl)
 	return atomic_inc_return(&tl->next_seqno);
 }
 
-static int __i915_sw_fence_call
-submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
+void __i915_gem_request_submit(struct drm_i915_gem_request *request)
 {
-	struct drm_i915_gem_request *request =
-		container_of(fence, typeof(*request), submit);
 	struct intel_engine_cs *engine = request->engine;
 	struct intel_timeline *timeline;
-	unsigned long flags;
 	u32 seqno;
 
-	if (state != FENCE_COMPLETE)
-		return NOTIFY_DONE;
-
 	/* Transfer from per-context onto the global per-engine timeline */
 	timeline = engine->timeline;
 	GEM_BUG_ON(timeline == request->timeline);
-
-	/* Will be called from irq-context when using foreign DMA fences */
-	spin_lock_irqsave(&timeline->lock, flags);
+	assert_spin_locked(&timeline->lock);
 
 	seqno = timeline_get_seqno(timeline->common);
 	GEM_BUG_ON(!seqno);
@@ -344,15 +335,36 @@ submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
 	GEM_BUG_ON(!request->global_seqno);
 	engine->emit_breadcrumb(request,
 				request->ring->vaddr + request->postfix);
-	engine->submit_request(request);
 
 	spin_lock(&request->timeline->lock);
 	list_move_tail(&request->link, &timeline->requests);
 	spin_unlock(&request->timeline->lock);
 
 	i915_sw_fence_commit(&request->execute);
+}
+
+void i915_gem_request_submit(struct drm_i915_gem_request *request)
+{
+	struct intel_engine_cs *engine = request->engine;
+	unsigned long flags;
 
-	spin_unlock_irqrestore(&timeline->lock, flags);
+	/* Will be called from irq-context when using foreign fences. */
+	spin_lock_irqsave(&engine->timeline->lock, flags);
+
+	__i915_gem_request_submit(request);
+
+	spin_unlock_irqrestore(&engine->timeline->lock, flags);
+}
+
+static int __i915_sw_fence_call
+submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
+{
+	if (state == FENCE_COMPLETE) {
+		struct drm_i915_gem_request *request =
+			container_of(fence, typeof(*request), submit);
+
+		request->engine->submit_request(request);
+	}
 
 	return NOTIFY_DONE;
 }

drivers/gpu/drm/i915/i915_gem_request.h

@@ -232,6 +232,9 @@ void __i915_add_request(struct drm_i915_gem_request *req, bool flush_caches);
 #define i915_add_request_no_flush(req) \
 	__i915_add_request(req, false)
 
+void __i915_gem_request_submit(struct drm_i915_gem_request *request);
+void i915_gem_request_submit(struct drm_i915_gem_request *request);
+
 struct intel_rps_client;
 #define NO_WAITBOOST ERR_PTR(-1)
 #define IS_RPS_CLIENT(p) (!IS_ERR(p))

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -629,11 +629,23 @@ static int guc_ring_doorbell(struct i915_guc_client *gc)
 static void i915_guc_submit(struct drm_i915_gem_request *rq)
 {
 	struct drm_i915_private *dev_priv = rq->i915;
-	unsigned int engine_id = rq->engine->id;
+	struct intel_engine_cs *engine = rq->engine;
+	unsigned int engine_id = engine->id;
 	struct intel_guc *guc = &rq->i915->guc;
 	struct i915_guc_client *client = guc->execbuf_client;
 	int b_ret;
 
+	/* We keep the previous context alive until we retire the following
+	 * request. This ensures that any the context object is still pinned
+	 * for any residual writes the HW makes into it on the context switch
+	 * into the next object following the breadcrumb. Otherwise, we may
+	 * retire the context too early.
+	 */
+	rq->previous_context = engine->last_context;
+	engine->last_context = rq->ctx;
+
+	i915_gem_request_submit(rq);
+
 	spin_lock(&client->wq_lock);
 	guc_wq_item_append(client, rq);
 

drivers/gpu/drm/i915/intel_lrc.c

@@ -434,6 +434,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 {
 	struct drm_i915_gem_request *cursor, *last;
 	struct execlist_port *port = engine->execlist_port;
+	unsigned long flags;
 	bool submit = false;
 
 	last = port->request;
@@ -469,6 +470,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 	 * and context switches) submission.
 	 */
 
+	spin_lock_irqsave(&engine->timeline->lock, flags);
 	spin_lock(&engine->execlist_lock);
 	list_for_each_entry(cursor, &engine->execlist_queue, execlist_link) {
 		/* Can we combine this request with the current port? It has to
@@ -501,6 +503,17 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 			i915_gem_request_assign(&port->request, last);
 			port++;
 		}
+
+		/* We keep the previous context alive until we retire the
+		 * following request. This ensures that any the context object
+		 * is still pinned for any residual writes the HW makes into it
+		 * on the context switch into the next object following the
+		 * breadcrumb. Otherwise, we may retire the context too early.
+		 */
+		cursor->previous_context = engine->last_context;
+		engine->last_context = cursor->ctx;
+
+		__i915_gem_request_submit(cursor);
 		last = cursor;
 		submit = true;
 	}
@@ -512,6 +525,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 		i915_gem_request_assign(&port->request, last);
 	}
 	spin_unlock(&engine->execlist_lock);
+	spin_unlock_irqrestore(&engine->timeline->lock, flags);
 
 	if (submit)
 		execlists_submit_ports(engine);
@@ -621,15 +635,6 @@ static void execlists_submit_request(struct drm_i915_gem_request *request)
 
 	spin_lock_irqsave(&engine->execlist_lock, flags);
 
-	/* We keep the previous context alive until we retire the following
-	 * request. This ensures that any the context object is still pinned
-	 * for any residual writes the HW makes into it on the context switch
-	 * into the next object following the breadcrumb. Otherwise, we may
-	 * retire the context too early.
-	 */
-	request->previous_context = engine->last_context;
-	engine->last_context = request->ctx;
-
 	list_add_tail(&request->execlist_link, &engine->execlist_queue);
 	if (execlists_elsp_idle(engine))
 		tasklet_hi_schedule(&engine->irq_tasklet);

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1294,6 +1294,8 @@ static void i9xx_submit_request(struct drm_i915_gem_request *request)
 {
 	struct drm_i915_private *dev_priv = request->i915;
 
+	i915_gem_request_submit(request);
+
 	I915_WRITE_TAIL(request->engine, request->tail);
 }