drm/i915: Throw away the active object retirement complexity

Remove the accumulated optimisations that we have for i915_vma_retire
and reduce it to the bare essential of tracking the active object
reference. This allows us to only use atomic operations, and so will be
able to avoid the struct_mutex requirement.

The principal loss here is the shrinker MRU bumping, so now if we have
to shrink, we will do so in much more random order and more likely to
try and shrink recently used objects. That is a nuisance, but shrinking
active objects is a second step we try to avoid and will always be a
system-wide performance issue.

The other loss is here is in the automatic pruning of the
reservation_object when idling. This is not as large an issue as upon
reservation_object introduction as now adding new fences into the object
replaces already signaled fences, keeping the array compact. But we do
lose the auto-expiration of stale fences and unused arrays. That may be
a noticeable problem for which we need to re-implement autopruning.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621183801.23252-3-chris@chris-wilson.co.uk

1 files changed, 17 insertions, 25 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_batch_pool.c b/drivers/gpu/drm/i915/i915_gem_batch_pool.c
index 25a3e4d09a2f..b17f23991253 100644
--- a/drivers/gpu/drm/i915/i915_gem_batch_pool.c
+++ b/drivers/gpu/drm/i915/i915_gem_batch_pool.c
@@ -94,34 +94,26 @@ i915_gem_batch_pool_get(struct i915_gem_batch_pool *pool,
 	list = &pool->cache_list[n];
 
 	list_for_each_entry(obj, list, batch_pool_link) {
+		struct reservation_object *resv = obj->base.resv;
+
 		/* The batches are strictly LRU ordered */
-		if (i915_gem_object_is_active(obj)) {
-			struct reservation_object *resv = obj->base.resv;
-
-			if (!reservation_object_test_signaled_rcu(resv, true))
-				break;
-
-			i915_retire_requests(pool->engine->i915);
-			GEM_BUG_ON(i915_gem_object_is_active(obj));
-
-			/*
-			 * The object is now idle, clear the array of shared
-			 * fences before we add a new request. Although, we
-			 * remain on the same engine, we may be on a different
-			 * timeline and so may continually grow the array,
-			 * trapping a reference to all the old fences, rather
-			 * than replace the existing fence.
-			 */
-			if (rcu_access_pointer(resv->fence)) {
-				reservation_object_lock(resv, NULL);
-				reservation_object_add_excl_fence(resv, NULL);
-				reservation_object_unlock(resv);
-			}
+		if (!reservation_object_test_signaled_rcu(resv, true))
+			break;
+
+		/*
+		 * The object is now idle, clear the array of shared
+		 * fences before we add a new request. Although, we
+		 * remain on the same engine, we may be on a different
+		 * timeline and so may continually grow the array,
+		 * trapping a reference to all the old fences, rather
+		 * than replace the existing fence.
+		 */
+		if (rcu_access_pointer(resv->fence)) {
+			reservation_object_lock(resv, NULL);
+			reservation_object_add_excl_fence(resv, NULL);
+			reservation_object_unlock(resv);
 		}
 
-		GEM_BUG_ON(!reservation_object_test_signaled_rcu(obj->base.resv,
-								 true));
-
 		if (obj->base.size >= size)
 			goto found;
 	}