[PATCH 04/25] drm/i915: Remove completed fences after a wait

[Chris Wilson]

If we wait up on the full (i.e. all shared fences, or upon an exclusive fence)
reservation object successfully, we know that all fences beneath it have
been signaled, so long as no new fences were added whilst we slept. If the
reservation_object remains the same, as detected by its seqcount, we can
then reap all the fences upon completion.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 5f7b8c88eb7e..d93032875f28 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -427,7 +427,9 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 				 long timeout,
 				 struct intel_rps_client *rps)
 {
+	unsigned int seq = __read_seqcount_begin(&resv->seq);
 	struct dma_fence *excl;
+	bool prune_fences = false;
 
 	if (flags & I915_WAIT_ALL) {
 		struct dma_fence **shared;
@@ -452,15 +454,26 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
 		for (; i < count; i++)
 			dma_fence_put(shared[i]);
 		kfree(shared);
+
+		prune_fences = count && timeout >= 0;
 	} else {
 		excl = reservation_object_get_excl_rcu(resv);
 	}
 
-	if (excl && timeout >= 0)
+	if (excl && timeout >= 0) {
 		timeout = i915_gem_object_wait_fence(excl, flags, timeout, rps);
+		prune_fences = timeout >= 0;
+	}
 
 	dma_fence_put(excl);
 
+	if (prune_fences && !__read_seqcount_retry(&resv->seq, seq)) {
+		reservation_object_lock(resv, NULL);
+		if (!__read_seqcount_retry(&resv->seq, seq))
+			reservation_object_add_excl_fence(resv, NULL);
+		reservation_object_unlock(resv);
+	}
+
 	return timeout;
 }
 
-- 
2.11.0