[Intel-gfx] [PATCH 03/66] drm/i915: Remove requirement for holding i915_request.lock for breadcrumbs

[Chris Wilson <chris@chris-wilson.co.uk>]

Since the breadcrumb enabling/cancelling itself is serialised by the
breadcrumbs.irq_lock, with a bit of care we can remove the outer
serialisation with i915_request.lock for concurrent
dma_fence_enable_signaling(). This has the important side-effect of
eliminating the nested i915_request.lock within request submission.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 100 +++++++++++---------
 drivers/gpu/drm/i915/gt/intel_lrc.c         |  14 ---
 drivers/gpu/drm/i915/i915_request.c         |  30 ++----
 3 files changed, 63 insertions(+), 81 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index 91786310c114..87fd06d3eb3f 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -220,17 +220,17 @@ static void signal_irq_work(struct irq_work *work)
 	}
 }
 
-static bool __intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
+static void __intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
 {
 	struct intel_engine_cs *engine =
 		container_of(b, struct intel_engine_cs, breadcrumbs);
 
 	lockdep_assert_held(&b->irq_lock);
 	if (b->irq_armed)
-		return true;
+		return;
 
 	if (!intel_gt_pm_get_if_awake(engine->gt))
-		return false;
+		return;
 
 	/*
 	 * The breadcrumb irq will be disarmed on the interrupt after the
@@ -250,8 +250,6 @@ static bool __intel_breadcrumbs_arm_irq(struct intel_breadcrumbs *b)
 
 	if (!b->irq_enabled++)
 		irq_enable(engine);
-
-	return true;
 }
 
 void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
@@ -310,57 +308,69 @@ void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
 {
 }
 
-bool i915_request_enable_breadcrumb(struct i915_request *rq)
+static void insert_breadcrumb(struct i915_request *rq,
+			      struct intel_breadcrumbs *b)
 {
-	lockdep_assert_held(&rq->lock);
+	struct intel_context *ce = rq->context;
+	struct list_head *pos;
 
-	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &rq->fence.flags))
-		return true;
+	if (test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))
+		return;
 
-	if (test_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags)) {
-		struct intel_breadcrumbs *b = &rq->engine->breadcrumbs;
-		struct intel_context *ce = rq->context;
-		struct list_head *pos;
+	__intel_breadcrumbs_arm_irq(b);
 
-		spin_lock(&b->irq_lock);
+	/*
+	 * We keep the seqno in retirement order, so we can break
+	 * inside intel_engine_signal_breadcrumbs as soon as we've
+	 * passed the last completed request (or seen a request that
+	 * hasn't event started). We could walk the timeline->requests,
+	 * but keeping a separate signalers_list has the advantage of
+	 * hopefully being much smaller than the full list and so
+	 * provides faster iteration and detection when there are no
+	 * more interrupts required for this context.
+	 *
+	 * We typically expect to add new signalers in order, so we
+	 * start looking for our insertion point from the tail of
+	 * the list.
+	 */
+	list_for_each_prev(pos, &ce->signals) {
+		struct i915_request *it =
+			list_entry(pos, typeof(*it), signal_link);
+
+		if (i915_seqno_passed(rq->fence.seqno, it->fence.seqno))
+			break;
+	}
+	list_add(&rq->signal_link, pos);
+	if (pos == &ce->signals) /* catch transitions from empty list */
+		list_move_tail(&ce->signal_link, &b->signalers);
+	GEM_BUG_ON(!check_signal_order(ce, rq));
 
-		if (test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))
-			goto unlock;
+	set_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags);
+}
 
-		if (!__intel_breadcrumbs_arm_irq(b))
-			goto unlock;
+bool i915_request_enable_breadcrumb(struct i915_request *rq)
+{
+	struct intel_breadcrumbs *b;
 
-		/*
-		 * We keep the seqno in retirement order, so we can break
-		 * inside intel_engine_signal_breadcrumbs as soon as we've
-		 * passed the last completed request (or seen a request that
-		 * hasn't event started). We could walk the timeline->requests,
-		 * but keeping a separate signalers_list has the advantage of
-		 * hopefully being much smaller than the full list and so
-		 * provides faster iteration and detection when there are no
-		 * more interrupts required for this context.
-		 *
-		 * We typically expect to add new signalers in order, so we
-		 * start looking for our insertion point from the tail of
-		 * the list.
-		 */
-		list_for_each_prev(pos, &ce->signals) {
-			struct i915_request *it =
-				list_entry(pos, typeof(*it), signal_link);
+	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &rq->fence.flags))
+		return true;
 
-			if (i915_seqno_passed(rq->fence.seqno, it->fence.seqno))
-				break;
-		}
-		list_add(&rq->signal_link, pos);
-		if (pos == &ce->signals) /* catch transitions from empty list */
-			list_move_tail(&ce->signal_link, &b->signalers);
-		GEM_BUG_ON(!check_signal_order(ce, rq));
+	if (!test_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags))
+		return true;
 
-		set_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags);
-unlock:
+	b = &READ_ONCE(rq->engine)->breadcrumbs;
+	spin_lock(&b->irq_lock);
+	while (unlikely(b != &READ_ONCE(rq->engine)->breadcrumbs)) {
 		spin_unlock(&b->irq_lock);
+		b = &READ_ONCE(rq->engine)->breadcrumbs;
+		spin_lock(&b->irq_lock);
 	}
 
+	if (test_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags))
+		insert_breadcrumb(rq, b);
+
+	spin_unlock(&b->irq_lock);
+
 	return !__request_completed(rq);
 }
 
@@ -368,8 +378,6 @@ void i915_request_cancel_breadcrumb(struct i915_request *rq)
 {
 	struct intel_breadcrumbs *b = &rq->engine->breadcrumbs;
 
-	lockdep_assert_held(&rq->lock);
-
 	/*
 	 * We must wait for b->irq_lock so that we know the interrupt handler
 	 * has released its reference to the intel_context and has completed
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index e0280a672f1d..aa7be7f05f8c 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1148,20 +1148,6 @@ __unwind_incomplete_requests(struct intel_engine_cs *engine)
 		} else {
 			struct intel_engine_cs *owner = rq->context->engine;
 
-			/*
-			 * Decouple the virtual breadcrumb before moving it
-			 * back to the virtual engine -- we don't want the
-			 * request to complete in the background and try
-			 * and cancel the breadcrumb on the virtual engine
-			 * (instead of the old engine where it is linked)!
-			 */
-			if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
-				     &rq->fence.flags)) {
-				spin_lock_nested(&rq->lock,
-						 SINGLE_DEPTH_NESTING);
-				i915_request_cancel_breadcrumb(rq);
-				spin_unlock(&rq->lock);
-			}
 			WRITE_ONCE(rq->engine, owner);
 			owner->submit_request(rq);
 			active = NULL;
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index d13dd013acb4..29b5e71307e3 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -318,12 +318,13 @@ bool i915_request_retire(struct i915_request *rq)
 		dma_fence_signal_locked(&rq->fence);
 	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &rq->fence.flags))
 		i915_request_cancel_breadcrumb(rq);
+	spin_unlock_irq(&rq->lock);
+
+	__notify_execute_cb(rq);
 	if (i915_request_has_waitboost(rq)) {
 		GEM_BUG_ON(!atomic_read(&rq->engine->gt->rps.num_waiters));
 		atomic_dec(&rq->engine->gt->rps.num_waiters);
 	}
-	spin_unlock_irq(&rq->lock);
-	__notify_execute_cb(rq);
 
 	remove_from_client(rq);
 	__list_del_entry(&rq->link); /* poison neither prev/next (RCU walks) */
@@ -549,17 +550,9 @@ bool __i915_request_submit(struct i915_request *request)
 	}
 	__notify_execute_cb(request);
 
-	/* We may be recursing from the signal callback of another i915 fence */
-	if (!i915_request_signaled(request)) {
-		spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING);
-
-		if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
-			     &request->fence.flags) &&
-		    !i915_request_enable_breadcrumb(request))
-			intel_engine_signal_breadcrumbs(engine);
-
-		spin_unlock(&request->lock);
-	}
+	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags) &&
+	    !i915_request_enable_breadcrumb(request))
+		intel_engine_signal_breadcrumbs(engine);
 
 	return result;
 }
@@ -591,16 +584,11 @@ void __i915_request_unsubmit(struct i915_request *request)
 	 * is kept in seqno/ring order.
 	 */
 
-	/* We may be recursing from the signal callback of another i915 fence */
-	spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING);
-
-	if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags))
-		i915_request_cancel_breadcrumb(request);
-
 	GEM_BUG_ON(!test_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags));
-	clear_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags);
+	clear_bit_unlock(I915_FENCE_FLAG_ACTIVE, &request->fence.flags);
 
-	spin_unlock(&request->lock);
+	if (test_bit(I915_FENCE_FLAG_SIGNAL, &request->fence.flags))
+		i915_request_cancel_breadcrumb(request);
 
 	/* We've already spun, don't charge on resubmitting. */
 	if (request->sched.semaphores && i915_request_started(request))
-- 
2.20.1

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