[PATCH 2/2] drm/ttm: use RCU to pipeline evictions

[Christian König]

From: Christian König <christian.koe...@amd.com>

Could be faster on the read path.

Signed-off-by: Christian König <christian.koenig at amd.com>
---
 drivers/gpu/drm/ttm/ttm_bo.c      | 16 ++++++++++------
 drivers/gpu/drm/ttm/ttm_bo_util.c |  8 +++++---
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 66c50ad..7e30f3b 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -797,9 +797,11 @@ static int ttm_bo_add_move_fence(struct ttm_buffer_object 
*bo,
        struct fence *fence;
        int ret;

-       spin_lock(&man->move_lock);
-       fence = fence_get(man->move);
-       spin_unlock(&man->move_lock);
+       rcu_read_lock();
+       do
+               fence = rcu_dereference(man->move);
+       while (unlikely(fence && !fence_get_rcu(fence)));
+       rcu_read_unlock();

        if (fence) {
                reservation_object_add_shared_fence(bo->resv, fence);
@@ -1304,9 +1306,11 @@ static int ttm_bo_force_list_clean(struct ttm_bo_device 
*bdev,
        }
        spin_unlock(&glob->lru_lock);

-       spin_lock(&man->move_lock);
-       fence = fence_get(man->move);
-       spin_unlock(&man->move_lock);
+       rcu_read_lock();
+       do
+               fence = rcu_dereference(man->move);
+       while (unlikely(fence && !fence_get_rcu(fence)));
+       rcu_read_unlock();

        if (fence) {
                ret = fence_wait(fence, false);
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c 
b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 4da0e78..fcd2431 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -746,6 +746,7 @@ int ttm_bo_pipeline_move(struct ttm_buffer_object *bo,
                ttm_bo_unref(&ghost_obj);

        } else if (from->flags & TTM_MEMTYPE_FLAG_FIXED) {
+               struct fence *old;

                /**
                 * BO doesn't have a TTM we need to bind/unbind. Just remember
@@ -753,9 +754,10 @@ int ttm_bo_pipeline_move(struct ttm_buffer_object *bo,
                 */

                spin_lock(&from->move_lock);
-               if (!from->move || fence_is_later(fence, from->move)) {
-                       fence_put(from->move);
-                       from->move = fence_get(fence);
+               old = rcu_dereference_protected(from->move, 1);
+               if (!old || fence_is_later(fence, old)) {
+                       rcu_assign_pointer(from->move, fence_get(fence));
+                       fence_put(old);
                }
                spin_unlock(&from->move_lock);

-- 
2.5.0