[Intel-gfx] [PATCH 32/39] drm/i915/gt: Shrink the critical section for irq signaling

[Chris Wilson]

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 <ch...@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 5b84f51931d9..3e69d6c3b197 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -251,6 +251,7 @@ 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;
 
@@ -284,6 +285,7 @@ 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 6e57f30c80f0..f98d5fd81904 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1400,7 +1400,8 @@ 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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