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>
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index d1e5326..5f61f13 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -220,7 +220,7 @@
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 @@
return ret;
}
+ atomic_set(&bo->reserved, 1);
if (use_sequence) {
/**
* Wake up waiters that may need to recheck for deadlock,