[Intel-gfx] [PATCH] drm/i915: Skip execlists_dequeue() early if the list is empty

[Chris Wilson]

Do an early read of the execlists' queue before we take the spinlock and
start checking. This is safe as the first writer to the execlists queue
will cause the tasklet to be run again after a memory barrier.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Michał Winiarski <michal.winiarski at intel.com>
---

With the plan to kick the tasklet before it is ready, eliminating a few
of the heavier checks seems sensible.
-Chris

---
 drivers/gpu/drm/i915/intel_lrc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 89f38e7def9f..17342bc939ad 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -402,6 +402,9 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 	struct rb_node *rb;
 	bool submit = false;
 
+	if (!READ_ONCE(engine->execlist_first))
+		return;
+
 	last = port->request;
 	if (last)
 		/* WaIdleLiteRestore:bdw,skl
-- 
2.11.0