[Intel-gfx] [PATCH v2] drm/i915/gt: Transfer old virtual breadcrumbs to irq_worker

* [Intel-gfx] [PATCH v2] drm/i915/gt: Transfer old virtual breadcrumbs to irq_worker
@ 2020-05-12 13:22 Chris Wilson
  2020-05-12 14:23 ` [Intel-gfx] ✓ Fi.CI.BAT: success for " Patchwork
                   ` (6 more replies)
  0 siblings, 7 replies; 13+ messages in thread
From: Chris Wilson @ 2020-05-12 13:22 UTC (permalink / raw)
  To: intel-gfx; +Cc: Chris Wilson

The second try at staging the transfer of the breadcrumb. In part one,
we realised we could not simply move to the second engine as we were
only holding the breadcrumb lock on the first. So in commit 6c81e21a4742
("drm/i915/gt: Stage the transfer of the virtual breadcrumb"), we
removed it from the first engine and marked up this request to reattach
the signaling on the new engine. However, this failed to take into
account that we only attach the breadcrumb if the new request is added
at the start of the queue, which if we are transferring, it is because
we know there to be a request to be signaled (and hence we would not be
attached).

In this attempt, we try to transfer the completed requests to the
irq_worker on its rq->engine->breadcrumbs. This preserves the coupling
between the rq and its breadcrumbs, so that
i915_request_cancel_breadcrumb() does not attempt to manipulate the list
under the wrong lock.

Fixes: 6c81e21a4742 ("drm/i915/gt: Stage the transfer of the virtual breadcrumb")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
v2: rewrite from scratch with a new idea
---
 drivers/gpu/drm/i915/gt/intel_breadcrumbs.c  | 33 ++++++++++++++++++++
 drivers/gpu/drm/i915/gt/intel_engine.h       |  3 ++
 drivers/gpu/drm/i915/gt/intel_engine_types.h |  2 ++
 drivers/gpu/drm/i915/gt/intel_lrc.c          | 26 ++-------------
 4 files changed, 41 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index cbedba857d43..e09dc162b508 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -155,6 +155,8 @@ static void signal_irq_work(struct irq_work *work)
 	if (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));
 
@@ -255,6 +257,7 @@ void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
 
 	spin_lock_init(&b->irq_lock);
 	INIT_LIST_HEAD(&b->signalers);
+	INIT_LIST_HEAD(&b->signaled_requests);
 
 	init_irq_work(&b->irq_work, signal_irq_work);
 }
@@ -274,6 +277,36 @@ void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
 	spin_unlock_irqrestore(&b->irq_lock, flags);
 }
 
+void intel_engine_transfer_breadcrumbs(struct intel_engine_cs *engine,
+				       struct intel_context *ce)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+	unsigned long flags;
+
+	spin_lock_irqsave(&b->irq_lock, flags);
+	if (!list_empty(&ce->signals)) {
+		struct i915_request *rq, *next;
+
+		list_for_each_entry_safe(rq, next, &ce->signals, signal_link) {
+			GEM_BUG_ON(rq->engine != engine);
+			GEM_BUG_ON(!i915_request_completed(rq));
+
+			clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags);
+			if (!__dma_fence_signal(&rq->fence))
+				continue;
+
+			i915_request_get(rq);
+			list_add_tail(&rq->signal_link, &b->signaled_requests);
+		}
+
+		INIT_LIST_HEAD(&ce->signals);
+		list_del_init(&ce->signal_link);
+
+		irq_work_queue(&b->irq_work);
+	}
+	spin_unlock_irqrestore(&b->irq_lock, flags);
+}
+
 void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
 {
 }
diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
index cb789c8bf06b..45418f887953 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine.h
@@ -238,6 +238,9 @@ intel_engine_signal_breadcrumbs(struct intel_engine_cs *engine)
 void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine);
 void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
 
+void intel_engine_transfer_breadcrumbs(struct intel_engine_cs *engine,
+				       struct intel_context *ce);
+
 void intel_engine_print_breadcrumbs(struct intel_engine_cs *engine,
 				    struct drm_printer *p);
 
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
index c113b7805e65..e20b39eefd79 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -377,6 +377,8 @@ struct intel_engine_cs {
 		spinlock_t irq_lock;
 		struct list_head signalers;
 
+		struct list_head signaled_requests;
+
 		struct irq_work irq_work; /* for use from inside irq_lock */
 
 		unsigned int irq_enabled;
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 15716e4d6b76..ac32d494b07d 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1821,30 +1821,10 @@ static bool virtual_matches(const struct virtual_engine *ve,
 	return true;
 }
 
-static void virtual_xfer_breadcrumbs(struct virtual_engine *ve,
-				     struct i915_request *rq)
+static void virtual_xfer_breadcrumbs(struct virtual_engine *ve)
 {
-	struct intel_engine_cs *old = ve->siblings[0];
-
 	/* All unattached (rq->engine == old) must already be completed */
-
-	spin_lock(&old->breadcrumbs.irq_lock);
-	if (!list_empty(&ve->context.signal_link)) {
-		list_del_init(&ve->context.signal_link);
-
-		/*
-		 * We cannot acquire the new engine->breadcrumbs.irq_lock
-		 * (as we are holding a breadcrumbs.irq_lock already),
-		 * so attach this request to the signaler on submission.
-		 * The queued irq_work will occur when we finally drop
-		 * the engine->active.lock after dequeue.
-		 */
-		set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &rq->fence.flags);
-
-		/* Also transfer the pending irq_work for the old breadcrumb. */
-		intel_engine_signal_breadcrumbs(rq->engine);
-	}
-	spin_unlock(&old->breadcrumbs.irq_lock);
+	intel_engine_transfer_breadcrumbs(ve->siblings[0], &ve->context);
 }
 
 #define for_each_waiter(p__, rq__) \
@@ -2279,7 +2259,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 									engine);
 
 				if (!list_empty(&ve->context.signals))
-					virtual_xfer_breadcrumbs(ve, rq);
+					virtual_xfer_breadcrumbs(ve);
 
 				/*
 				 * Move the bound engine to the top of the list
-- 
2.20.1

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