[Intel-gfx] [PATCH] drm/i915/execlists: Don't merely skip submission if maybe timeslicing

[Chris Wilson]

Normally, we try and skip submission if ELSP[1] is filled. However, we
may desire to enable timeslicing due to the queue priority, even if
ELSP[1] itself does not require timeslicing. That is the queue is equal
priority to ELSP[0] and higher priority then ELSP[1]. Previously, we
would wait until the context switch to preempt the current ELSP[1], but
with timeslicing, we want to preempt ELSP[0] and replace it with the
queue.

Fixes: 2229adc81380 ("drm/i915/execlist: Trim immediate timeslice expiry")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 6620772edf4f..7690bc659b31 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1509,8 +1509,17 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 			 * submission.
 			 */
 			if (!list_is_last(&last->sched.link,
-					  &engine->active.requests))
+					  &engine->active.requests)) {
+				/*
+				 * Even if ELSP[1] is occupied and not worthy
+				 * of timeslices, our queue might be.
+				 */
+				if (!execlists->timer.expires &&
+				    need_timeslice(engine, last))
+					mod_timer(&execlists->timer,
+						  jiffies + 1);
 				return;
+			}
 
 			/*
 			 * WaIdleLiteRestore:bdw,skl
-- 
2.23.0