[PATCH 4/5] drm/ttm: Improved fencing of buffer object lists

[Thomas Hellstrom]

Drastically reduce the number of spin lock / unlock operations by performing
unreserving and fencing under global locks.

Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
---
 drivers/gpu/drm/ttm/ttm_bo.c           |   11 +++++++--
 drivers/gpu/drm/ttm/ttm_execbuf_util.c |   36 ++++++++++++++++++++++---------
 include/drm/ttm/ttm_bo_driver.h        |   10 ++++++++
 include/drm/ttm/ttm_execbuf_util.h     |    2 +
 4 files changed, 45 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index d93c73b..551a5d3 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -299,14 +299,19 @@ int ttm_bo_reserve(struct ttm_buffer_object *bo,
 	return ret;
 }
 
+void ttm_bo_unreserve_locked(struct ttm_buffer_object *bo)
+{
+	ttm_bo_add_to_lru(bo);
+	atomic_set(&bo->reserved, 0);
+	wake_up_all(&bo->event_queue);
+}
+
 void ttm_bo_unreserve(struct ttm_buffer_object *bo)
 {
 	struct ttm_bo_global *glob = bo->glob;
 
 	spin_lock(&glob->lru_lock);
-	ttm_bo_add_to_lru(bo);
-	atomic_set(&bo->reserved, 0);
-	wake_up_all(&bo->event_queue);
+	ttm_bo_unreserve_locked(bo);
 	spin_unlock(&glob->lru_lock);
 }
 EXPORT_SYMBOL(ttm_bo_unreserve);
diff --git a/drivers/gpu/drm/ttm/ttm_execbuf_util.c b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
index a3ae712..7646fb5 100644
--- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
+++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
@@ -195,22 +195,36 @@ EXPORT_SYMBOL(ttm_eu_reserve_buffers);
 void ttm_eu_fence_buffer_objects(struct list_head *list, void *sync_obj)
 {
 	struct ttm_validate_buffer *entry;
+	struct ttm_buffer_object *bo;
+	struct ttm_bo_global *glob;
+	struct ttm_bo_device *bdev;
+	struct ttm_bo_driver *driver;
 
-	list_for_each_entry(entry, list, head) {
-		struct ttm_buffer_object *bo = entry->bo;
-		struct ttm_bo_device *bdev = bo->bdev;
-		struct ttm_bo_driver *driver = bdev->driver;
-		void *old_sync_obj;
+	if (list_empty(list))
+		return;
+
+	bo = list_first_entry(list, struct ttm_validate_buffer, head)->bo;
+	bdev = bo->bdev;
+	driver = bdev->driver;
+	glob = bo->glob;
 
-		spin_lock(&bdev->fence_lock);
-		old_sync_obj = bo->sync_obj;
+	spin_lock(&bdev->fence_lock);
+	spin_lock(&glob->lru_lock);
+
+	list_for_each_entry(entry, list, head) {
+		bo = entry->bo;
+		entry->old_sync_obj = bo->sync_obj;
 		bo->sync_obj = driver->sync_obj_ref(sync_obj);
 		bo->sync_obj_arg = entry->new_sync_obj_arg;
-		spin_unlock(&bdev->fence_lock);
-		ttm_bo_unreserve(bo);
+		ttm_bo_unreserve_locked(bo);
 		entry->reserved = false;
-		if (old_sync_obj)
-			driver->sync_obj_unref(&old_sync_obj);
+	}
+	spin_unlock(&glob->lru_lock);
+	spin_unlock(&bdev->fence_lock);
+
+	list_for_each_entry(entry, list, head) {
+		if (entry->old_sync_obj)
+			driver->sync_obj_unref(&entry->old_sync_obj);
 	}
 }
 EXPORT_SYMBOL(ttm_eu_fence_buffer_objects);
diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
index ca8131e..cfb9ca4 100644
--- a/include/drm/ttm/ttm_bo_driver.h
+++ b/include/drm/ttm/ttm_bo_driver.h
@@ -910,6 +910,16 @@ extern int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
 extern void ttm_bo_unreserve(struct ttm_buffer_object *bo);
 
 /**
+ * ttm_bo_unreserve_locked
+ *
+ * @bo: A pointer to a struct ttm_buffer_object.
+ *
+ * Unreserve a previous reservation of @bo.
+ * Needs to be called with struct ttm_bo_global::lru_lock held.
+ */
+extern void ttm_bo_unreserve_locked(struct ttm_buffer_object *bo);
+
+/**
  * ttm_bo_wait_unreserved
  *
  * @bo: A pointer to a struct ttm_buffer_object.
diff --git a/include/drm/ttm/ttm_execbuf_util.h b/include/drm/ttm/ttm_execbuf_util.h
index fd09b84..535ab00 100644
--- a/include/drm/ttm/ttm_execbuf_util.h
+++ b/include/drm/ttm/ttm_execbuf_util.h
@@ -44,6 +44,7 @@
  * @reserved:       Indicates whether @bo has been reserved for validation.
  * @removed:        Indicates whether @bo has been removed from lru lists.
  * @put_count:      Number of outstanding references on bo::list_kref.
+ * @old_sync_obj:   Pointer to a sync object about to be unreferenced
  */
 
 struct ttm_validate_buffer {
@@ -53,6 +54,7 @@ struct ttm_validate_buffer {
 	bool reserved;
 	bool removed;
 	int put_count;
+	void *old_sync_obj;
 };
 
 /**
-- 
1.6.2.5