drm/i915: Remove completed fences after a wait

If we wait upon 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@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170217151304.16665-6-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 5f7b8c88eb7e6f804c102ec5916e8c316bbecb1d..d93032875f2865d5e890a04e54f321fd68aa64da 100644 (file)
--- 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;
 }