[PATCH 14/14] drm/i915/breadcrumbs: Convert the signal rbtree to the cached variant

[Chris Wilson]

As we keep track of the leftmost element of the rbtree ourselves, we can
simply switch over to the new library variant of rbtree that provides
the caching itself.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 24 +++++++++---------------
 drivers/gpu/drm/i915/intel_ringbuffer.h  |  4 ++--
 2 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 6cfffa68f71a..6dd6bc9811a8 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -663,13 +663,7 @@ static void __intel_engine_remove_signal(struct intel_engine_cs *engine,
 	 * the oldest before picking the next one.
 	 */
 	if (request->signaling.wait.seqno) {
-		if (request == rcu_access_pointer(b->first_signal)) {
-			struct rb_node *rb = rb_next(&request->signaling.node);
-			rcu_assign_pointer(b->first_signal,
-					   rb ? to_signaler(rb) : NULL);
-		}
-
-		rb_erase(&request->signaling.node, &b->signals);
+		rb_erase_cached(&request->signaling.node, &b->signals);
 		request->signaling.wait.seqno = 0;
 	}
 }
@@ -697,7 +691,9 @@ static int intel_breadcrumbs_signaler(void *arg)
 		 * a new client.
 		 */
 		rcu_read_lock();
-		request = rcu_dereference(b->first_signal);
+		request = rb_entry_safe(rb_first_cached(&b->signals),
+					struct drm_i915_gem_request,
+					signaling.node);
 		if (request)
 			request = i915_gem_request_get_rcu(request);
 		rcu_read_unlock();
@@ -790,7 +786,7 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request,
 		 */
 		parent = NULL;
 		first = true;
-		p = &b->signals.rb_node;
+		p = &b->signals.rb_root.rb_node;
 		while (*p) {
 			parent = *p;
 			if (i915_seqno_passed(seqno,
@@ -802,9 +798,8 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request,
 			}
 		}
 		rb_link_node(&request->signaling.node, parent, p);
-		rb_insert_color(&request->signaling.node, &b->signals);
-		if (first)
-			rcu_assign_pointer(b->first_signal, request);
+		rb_insert_color_cached(&request->signaling.node,
+				       &b->signals, first);
 	} else {
 		__intel_engine_remove_wait(engine, &request->signaling.wait);
 		request->signaling.wait.seqno = 0;
@@ -902,8 +897,7 @@ void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
 	/* The engines should be idle and all requests accounted for! */
 	WARN_ON(READ_ONCE(b->irq_wait));
 	WARN_ON(!RB_EMPTY_ROOT(&b->waiters));
-	WARN_ON(rcu_access_pointer(b->first_signal));
-	WARN_ON(!RB_EMPTY_ROOT(&b->signals));
+	WARN_ON(!RB_EMPTY_ROOT(&b->signals.rb_root));
 
 	if (!IS_ERR_OR_NULL(b->signaler))
 		kthread_stop(b->signaler);
@@ -923,7 +917,7 @@ bool intel_breadcrumbs_busy(struct intel_engine_cs *engine)
 		busy = true;
 	}
 
-	if (rcu_access_pointer(b->first_signal)) {
+	if (!RB_EMPTY_ROOT(&b->signals.rb_root)) {
 		wake_up_process(b->signaler);
 		busy = true;
 	}
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 0b762a4d4612..5dade4d144de 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -327,9 +327,9 @@ struct intel_engine_cs {
 
 		spinlock_t rb_lock; /* protects the rb and wraps irq_lock */
 		struct rb_root waiters; /* sorted by retirement, priority */
-		struct rb_root signals; /* sorted by retirement */
+		struct rb_root_cached signals; /* sorted by retirement */
+
 		struct task_struct *signaler; /* used for fence signalling */
-		struct drm_i915_gem_request __rcu *first_signal;
 		struct timer_list fake_irq; /* used after a missed interrupt */
 		struct timer_list hangcheck; /* detect missed interrupts */
 
-- 
2.15.1