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@xxxxxxxxxx>
---
drivers/gpu/drm/ttm/ttm_bo.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bf6e4b5..46008ea 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -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,
--
1.7.4.4
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