[PATCH 8/9] drm/i915/gt: Track signaled breadcrumbs outside of the breadcrumb spinlock

[Chris Wilson]

Make b->signaled_requests a lockless-list so that we can manipulate it
outside of the b->irq_lock.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_breadcrumbs.c   | 42 +++++++++----------
 .../gpu/drm/i915/gt/intel_breadcrumbs_types.h |  2 +-
 drivers/gpu/drm/i915/i915_request.h           |  6 ++-
 3 files changed, 26 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index b4624895f4f3..53398a88126e 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -172,32 +172,23 @@ static void add_retire(struct intel_breadcrumbs *b, struct intel_timeline *tl)
 		intel_engine_add_retire(b->irq_engine, tl);
 }
 
-static bool __signal_request(struct i915_request *rq, struct list_head *signals)
-{
-	clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags);
-
-	if (!__dma_fence_signal(&rq->fence))
-		return false;
-
-	list_add_tail(&rq->signal_link, signals);
-	return true;
-}
-
 static void signal_irq_work(struct irq_work *work)
 {
 	struct intel_breadcrumbs *b = container_of(work, typeof(*b), irq_work);
 	const ktime_t timestamp = ktime_get();
+	struct llist_node *signal, *sn;
 	struct intel_context *ce, *cn;
 	struct list_head *pos, *next;
-	LIST_HEAD(signal);
+
+	signal = NULL;
+	if (!llist_empty(&b->signaled_requests))
+		signal = llist_del_all(&b->signaled_requests);
 
 	spin_lock(&b->irq_lock);
 
-	if (b->irq_armed && list_empty(&b->signalers))
+	if (!signal && b->irq_armed && list_empty(&b->signalers))
 		__intel_breadcrumbs_disarm_irq(b);
 
-	list_splice_init(&b->signaled_requests, &signal);
-
 	list_for_each_entry_safe(ce, cn, &b->signalers, signal_link) {
 		GEM_BUG_ON(list_empty(&ce->signals));
 
@@ -215,8 +206,13 @@ static void signal_irq_work(struct irq_work *work)
 			 * spinlock as the callback chain may end up adding
 			 * more signalers to the same context or engine.
 			 */
-			if (!__signal_request(rq, &signal))
+			clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags);
+			if (__dma_fence_signal(&rq->fence)) {
+				rq->signal_node.next = signal;
+				signal = &rq->signal_node;
+			} else {
 				i915_request_put(rq);
+			}
 		}
 
 		/*
@@ -236,9 +232,9 @@ static void signal_irq_work(struct irq_work *work)
 
 	spin_unlock(&b->irq_lock);
 
-	list_for_each_safe(pos, next, &signal) {
+	llist_for_each_safe(signal, sn, signal) {
 		struct i915_request *rq =
-			list_entry(pos, typeof(*rq), signal_link);
+			llist_entry(signal, typeof(*rq), signal_node);
 		struct list_head cb_list;
 
 		spin_lock(&rq->lock);
@@ -262,7 +258,7 @@ intel_breadcrumbs_create(struct intel_engine_cs *irq_engine)
 
 	spin_lock_init(&b->irq_lock);
 	INIT_LIST_HEAD(&b->signalers);
-	INIT_LIST_HEAD(&b->signaled_requests);
+	init_llist_head(&b->signaled_requests);
 
 	init_irq_work(&b->irq_work, signal_irq_work);
 
@@ -325,10 +321,12 @@ static void insert_breadcrumb(struct i915_request *rq,
 	 * its signal completion.
 	 */
 	if (__request_completed(rq)) {
-		if (__signal_request(rq, &b->signaled_requests))
-			irq_work_queue(&b->irq_work);
-		else
+		if (__dma_fence_signal(&rq->fence)) {
+			if (llist_add(&rq->signal_node, &b->signaled_requests))
+				irq_work_queue(&b->irq_work);
+		} else {
 			i915_request_put(rq);
+		}
 		return;
 	}
 
diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h b/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h
index 8e53b9942695..3fa19820b37a 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h
@@ -35,7 +35,7 @@ struct intel_breadcrumbs {
 	struct intel_engine_cs *irq_engine;
 
 	struct list_head signalers;
-	struct list_head signaled_requests;
+	struct llist_head signaled_requests;
 
 	struct irq_work irq_work; /* for use from inside irq_lock */
 
diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
index 16b721080195..874af6db6103 100644
--- a/drivers/gpu/drm/i915/i915_request.h
+++ b/drivers/gpu/drm/i915/i915_request.h
@@ -176,7 +176,11 @@ struct i915_request {
 	struct intel_context *context;
 	struct intel_ring *ring;
 	struct intel_timeline __rcu *timeline;
-	struct list_head signal_link;
+
+	union {
+		struct list_head signal_link;
+		struct llist_node signal_node;
+	};
 
 	/*
 	 * The rcu epoch of when this request was allocated. Used to judiciously
-- 
2.20.1