drm/ttm/radeon/nouveau: Kill the bo lock in favour of a bo device fence_lock

The bo lock used only to protect the bo sync object members, and since it
is a per bo lock, fencing a buffer list will see a lot of locks and unlocks.
Replace it with a per-device lock that protects the sync object members on
*all* bos. Reading and setting these members will always be very quick, so
the risc of heavy lock contention is microscopic. Note that waiting for
sync objects will always take place outside of this lock.

The bo device fence lock will eventually be replaced with a seqlock /
rcu mechanism so we can determine that a bo is idle under a
rcu / read seqlock.

However this change will allow us to batch fencing and unreserving of
buffers with a minimal amount of locking.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jerome Glisse <j.glisse@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

2 files changed, 5 insertions, 4 deletions

diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index b0fc9c12554b..edacd483c59c 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -154,7 +154,6 @@ struct ttm_tt;
  * keeps one refcount. When this refcount reaches zero,
  * the object is destroyed.
  * @event_queue: Queue for processes waiting on buffer object status change.
- * @lock: spinlock protecting mostly synchronization members.
  * @mem: structure describing current placement.
  * @persistant_swap_storage: Usually the swap storage is deleted for buffers
  * pinned in physical memory. If this behaviour is not desired, this member
@@ -213,7 +212,6 @@ struct ttm_buffer_object {
         struct kref kref;
         struct kref list_kref;
         wait_queue_head_t event_queue;
-        spinlock_t lock;
 
         /**
          * Members protected by the bo::reserved lock.
@@ -248,10 +246,10 @@ struct ttm_buffer_object {
         atomic_t reserved;
 
         /**
-         * Members protected by the bo::lock
+         * Members protected by struct buffer_object_device::fence_lock
          * In addition, setting sync_obj to anything else
          * than NULL requires bo::reserved to be held. This allows for
-         * checking NULL while reserved but not holding bo::lock.
+         * checking NULL while reserved but not holding the mentioned lock.
          */
 
         void *sync_obj_arg;
diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
index 1e25a40c688e..ca8131e98300 100644
--- a/include/drm/ttm/ttm_bo_driver.h
+++ b/include/drm/ttm/ttm_bo_driver.h
@@ -510,6 +510,8 @@ struct ttm_bo_global {
  *
  * @driver: Pointer to a struct ttm_bo_driver struct setup by the driver.
  * @man: An array of mem_type_managers.
+ * @fence_lock: Protects the synchronizing members on *all* bos belonging
+ * to this device.
  * @addr_space_mm: Range manager for the device address space.
  * lru_lock: Spinlock that protects the buffer+device lru lists and
  * ddestroy lists.
@@ -531,6 +533,7 @@ struct ttm_bo_device {
         struct ttm_bo_driver *driver;
         rwlock_t vm_lock;
         struct ttm_mem_type_manager man[TTM_NUM_MEM_TYPES];
+        spinlock_t fence_lock;
         /*
          * Protected by the vm lock.
          */