Commit 6c1e963c authored Nov 06, 2012 by Thomas Hellstrom Committed by Dave Airlie Nov 20, 2012

drm/ttm: Optimize reservation slightly



Reservation locking currently always takes place under the LRU spinlock.
Hence, strictly there is no need for an atomic_cmpxchg call; we can use
atomic_read followed by atomic_write since nobody else will ever reserve
without the lru spinlock held.
At least on Intel this should remove a locked bus cycle on successful
reserve.

Note that thit commit may be obsoleted by the cross-device reservation work.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

parent cdad0521

drivers/gpu/drm/ttm/ttm_bo.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -220,7 +220,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
		struct ttm_bo_global *glob = bo->glob;
		int ret;

		while (unlikely(atomic_cmpxchg(&bo->reserved, 0, 1) != 0)) {
		while (unlikely(atomic_read(&bo->reserved) != 0)) {
		/**
		* Deadlock avoidance for multi-bo reserving.
		*/
		@@ -249,6 +249,7 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
		return ret;
		}

		atomic_set(&bo->reserved, 1);
		if (use_sequence) {
		/**
		* Wake up waiters that may need to recheck for deadlock,