[Intel-gfx] [PATCH] drm/i915/execlists: Avoid kicking the submission too early for rescheduling

[Chris Wilson]

If the request is still waiting on external fences, it has not yet been
submitted to the HW queue and so we can forgo kicking the submission
tasklet when re-evaluating its priority.

This should have no impact other than reducing the number of tasklet
wakeups under signal heavy workloads (e.g. switching between engines).

References: f6322eddaff7 ("drm/i915/preemption: Allow preemption between submission ports")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski at intel.com>
Cc: Michel Thierry <michel.thierry at intel.com>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/intel_lrc.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index b4ab06b05e58..08d8ac9d1f8f 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1051,12 +1051,16 @@ static void queue_request(struct intel_engine_cs *engine,
 	list_add_tail(&pt->link, &lookup_priolist(engine, pt, prio)->requests);
 }
 
-static void submit_queue(struct intel_engine_cs *engine, int prio)
+static void __submit_queue(struct intel_engine_cs *engine, int prio)
 {
-	if (prio > engine->execlists.queue_priority) {
 		engine->execlists.queue_priority = prio;
 		tasklet_hi_schedule(&engine->execlists.tasklet);
-	}
+}
+
+static void submit_queue(struct intel_engine_cs *engine, int prio)
+{
+	if (prio > engine->execlists.queue_priority)
+		__submit_queue(engine, prio);
 }
 
 static void execlists_submit_request(struct i915_request *request)
@@ -1189,7 +1193,14 @@ static void execlists_schedule(struct i915_request *request, int prio)
 			__list_del_entry(&pt->link);
 			queue_request(engine, pt, prio);
 		}
-		submit_queue(engine, prio);
+
+		if (prio > engine->execlists.queue_priority) {
+			struct i915_request *rq =
+				container_of(pt, typeof(*rq), priotree);
+
+			if (i915_sw_fence_done(&rq->submit))
+				__submit_queue(engine, prio);
+		}
 	}
 
 	spin_unlock_irq(&engine->timeline->lock);
-- 
2.16.3