dma-fence: Store the timestamp in the same union as the cb_list

The timestamp and the cb_list are mutually exclusive, the cb_list can
only be added to prior to being signaled (and once signaled we drain),
while the timestamp is only valid upon being signaled. Both the
timestamp and the cb_list are only valid while the fence is alive, and
as soon as no references are held can be replaced by the rcu_head.

By reusing the union for the timestamp, we squeeze the base dma_fence
struct to 64 bytes on x86-64.

v2: Sort the union chronologically

Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>.
Link: https://patchwork.freedesktop.org/patch/msgid/20190817153022.5749-1-chris@chris-wilson.co.uk

1 files changed, 7 insertions, 6 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index c092bdf5f0bf..ea56b2cc6095 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -112,18 +112,18 @@ __dma_fence_signal__timestamp(struct dma_fence *fence, ktime_t timestamp)
 }
 
 static void
-__dma_fence_signal__notify(struct dma_fence *fence)
+__dma_fence_signal__notify(struct dma_fence *fence,
+			   const struct list_head *list)
 {
 	struct dma_fence_cb *cur, *tmp;
 
 	lockdep_assert_held(fence->lock);
 	lockdep_assert_irqs_disabled();
 
-	list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
+	list_for_each_entry_safe(cur, tmp, list, node) {
 		INIT_LIST_HEAD(&cur->node);
 		cur->func(fence, cur);
 	}
-	INIT_LIST_HEAD(&fence->cb_list);
 }
 
 void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine)
@@ -185,11 +185,12 @@ void intel_engine_breadcrumbs_irq(struct intel_engine_cs *engine)
 	list_for_each_safe(pos, next, &signal) {
 		struct i915_request *rq =
 			list_entry(pos, typeof(*rq), signal_link);
-
-		__dma_fence_signal__timestamp(&rq->fence, timestamp);
+		struct list_head cb_list;
 
 		spin_lock(&rq->lock);
-		__dma_fence_signal__notify(&rq->fence);
+		list_replace(&rq->fence.cb_list, &cb_list);
+		__dma_fence_signal__timestamp(&rq->fence, timestamp);
+		__dma_fence_signal__notify(&rq->fence, &cb_list);
 		spin_unlock(&rq->lock);
 
 		i915_request_put(rq);