Cleanup work in the preceding commit added locking to
drm_sched_entity_pop_job(). This cleanup causes a slightly sub-optimal
lock cycle with drm_sched_rq_pop_entity().
sched_entity also utilizes the lockless spsc_queue (partially already
used simultaneously with locks), which was marked for removal in
commit 6e7eb171ac96 ("Documentation: drm: Add entry for removing spsc_queue to
TODO list")
To remove the lock-cycle mentioned above, the unlock must be moved
downwards, also locking the lockless queue.
Guard spsc_queue_pop() in drm_sched_entity_pop_job() with the lock and
document why that is being done.
Signed-off-by: Philipp Stanner <[email protected]>
---
drivers/gpu/drm/scheduler/sched_entity.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/scheduler/sched_entity.c
b/drivers/gpu/drm/scheduler/sched_entity.c
index 91aec20611ad..5cf0af91faf2 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -529,9 +529,17 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct
drm_sched_entity *entity)
spin_lock(&entity->lock);
prev_last_scheduled = entity->last_scheduled;
entity->last_scheduled = dma_fence_get(&sched_job->s_fence->finished);
- spin_unlock(&entity->lock);
+ /* Preceding cleanup work made it necessary to add the spinlock
+ * to this function. spsc_queue, a lockless queue, is now
+ * counterintuitively guarded by the lock as well. spsc_queue is queued
+ * for removal (see DRM TODO list), so this somewhat serves as a
+ * preparational step.
+ *
+ * TODO: Replace spsc_queue completely with a locked (h)list.
+ */
spsc_queue_pop(&entity->job_queue);
+ spin_unlock(&entity->lock);
dma_fence_put(prev_last_scheduled);
drm_sched_rq_pop_entity(entity);
--
2.54.0
