[Intel-gfx] [PATCH 07/10] drm/i915/gt: Shrink the critical section for irq signaling

From: Chris Wilson <chris@chris-wilson.co.uk>
To: intel-gfx@lists.freedesktop.org
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Subject: [Intel-gfx] [PATCH 07/10] drm/i915/gt: Shrink the critical section for irq signaling
Date: Tue,  1 Dec 2020 10:06:23 +0000	[thread overview]
Message-ID: <20201201100626.16073-7-chris@chris-wilson.co.uk> (raw)
In-Reply-To: <20201201100626.16073-1-chris@chris-wilson.co.uk>

Let's only wait for the list iterator when decoupling the virtual
breadcrumb, as the signaling of all the requests may take a long time,
during which we do not want to keep the tasklet spinning.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_breadcrumbs.c       | 2 ++
 drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h | 1 +
 drivers/gpu/drm/i915/gt/intel_lrc.c               | 3 ++-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index 63900edbde88..ac1e5f6c3c2c 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -239,6 +239,7 @@ static void signal_irq_work(struct irq_work *work)
 		intel_breadcrumbs_disarm_irq(b);
 
 	rcu_read_lock();
+	atomic_inc(&b->signaler_active);
 	list_for_each_entry_rcu(ce, &b->signalers, signal_link) {
 		struct i915_request *rq;
 
@@ -274,6 +275,7 @@ static void signal_irq_work(struct irq_work *work)
 			}
 		}
 	}
+	atomic_dec(&b->signaler_active);
 	rcu_read_unlock();
 
 	llist_for_each_safe(signal, sn, signal) {
diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h b/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h
index a74bb3062bd8..f672053d694d 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs_types.h
@@ -35,6 +35,7 @@ struct intel_breadcrumbs {
 	spinlock_t signalers_lock; /* protects the list of signalers */
 	struct list_head signalers;
 	struct llist_head signaled_requests;
+	atomic_t signaler_active;
 
 	spinlock_t irq_lock; /* protects the interrupt from hardirq context */
 	struct irq_work irq_work; /* for use from inside irq_lock */
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index b45ff3d259a8..76c6f20af155 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1401,7 +1401,8 @@ static void kick_siblings(struct i915_request *rq, struct intel_context *ce)
 		 * ce->signal_link.
 		 */
 		i915_request_cancel_breadcrumb(rq);
-		irq_work_sync(&engine->breadcrumbs->irq_work);
+		while (atomic_read(&engine->breadcrumbs->signaler_active))
+			cpu_relax();
 	}
 
 	if (READ_ONCE(ve->request))
-- 
2.20.1

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