[PATCH] drm/i915: Always wakeup the next breadcrumb waiter

[Chris Wilson]

Whenever we advance from one completed waiter to the next, give it a
kick so that it can check to see if its seqno completed during the
switch. We used to rely on faking an interrupt to determine when the
wake up was required, but now the irq should always be enabled and so no
longer receive the kick when starting a new waiter.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 46 ++++++++++++--------------------
 1 file changed, 17 insertions(+), 29 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 235d4645a5cf..d48cbd66ae42 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -287,6 +287,19 @@ static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
 	wake_up_process(wait->tsk); /* implicit smp_wmb() */
 }
 
+static inline void __intel_breadcrumbs_next(struct intel_breadcrumbs *b,
+					    struct rb_node *next)
+{
+	/* As there is a delay between reading the current
+	 * seqno, processing the completed tasks and selecting
+	 * the next waiter, we may have missed the interrupt
+	 * and so need for the next bottom-half to wakeup.
+	 */
+	GEM_BUG_ON(!b->irq_armed);
+	b->first_wait = to_wait(next);
+	wake_up_process(to_wait(next)->tsk);
+}
+
 static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
 				    struct intel_wait *wait)
 {
@@ -357,21 +370,7 @@ static bool __intel_engine_add_wait(struct intel_engine_cs *engine,
 		GEM_BUG_ON(!next && !first);
 		if (next && next != &wait->node) {
 			GEM_BUG_ON(first);
-			b->first_wait = to_wait(next);
-			/* As there is a delay between reading the current
-			 * seqno, processing the completed tasks and selecting
-			 * the next waiter, we may have missed the interrupt
-			 * and so need for the next bottom-half to wakeup.
-			 *
-			 * Also as we enable the IRQ, we may miss the
-			 * interrupt for that seqno, so we have to wake up
-			 * the next bottom-half in order to do a coherent check
-			 * in case the seqno passed.
-			 */
-			__intel_breadcrumbs_enable_irq(b);
-			if (test_bit(ENGINE_IRQ_BREADCRUMB,
-				     &engine->irq_posted))
-				wake_up_process(to_wait(next)->tsk);
+			__intel_breadcrumbs_next(b, next);
 		}
 
 		do {
@@ -473,21 +472,10 @@ static void __intel_engine_remove_wait(struct intel_engine_cs *engine,
 			}
 		}
 
-		if (next) {
-			/* In our haste, we may have completed the first waiter
-			 * before we enabled the interrupt. Do so now as we
-			 * have a second waiter for a future seqno. Afterwards,
-			 * we have to wake up that waiter in case we missed
-			 * the interrupt, or if we have to handle an
-			 * exception rather than a seqno completion.
-			 */
-			b->first_wait = to_wait(next);
-			if (b->first_wait->seqno != wait->seqno)
-				__intel_breadcrumbs_enable_irq(b);
-			wake_up_process(b->first_wait->tsk);
-		} else {
+		if (next)
+			__intel_breadcrumbs_next(b, next);
+		else
 			b->first_wait = NULL;
-		}
 	} else {
 		GEM_BUG_ON(rb_first(&b->waiters) == &wait->node);
 	}
-- 
2.11.0