[PATCH 2/3] drm: Only bump object-reference count when adding first handle

[Chris Wilson]

We only need a single reference count for all handles (i.e. non-zero
obj->handle_count) and so can trim a few atomic operations by only
taking the reference on the first handle and dropping it after the last.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/drm_gem.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index a08176debc0e..ad955d7c99fd 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -220,6 +220,9 @@ static void drm_gem_object_exported_dma_buf_free(struct 
drm_gem_object *obj)
 static void
 drm_gem_object_handle_unreference_unlocked(struct drm_gem_object *obj)
 {
+       struct drm_device *dev = obj->dev;
+       bool final = false;
+
        if (WARN_ON(obj->handle_count == 0))
                return;

@@ -229,14 +232,16 @@ drm_gem_object_handle_unreference_unlocked(struct 
drm_gem_object *obj)
        * checked for a name
        */

-       mutex_lock(&obj->dev->object_name_lock);
+       mutex_lock(&dev->object_name_lock);
        if (--obj->handle_count == 0) {
                drm_gem_object_handle_free(obj);
                drm_gem_object_exported_dma_buf_free(obj);
+               final = true;
        }
-       mutex_unlock(&obj->dev->object_name_lock);
+       mutex_unlock(&dev->object_name_lock);

-       drm_gem_object_unreference_unlocked(obj);
+       if (final)
+               drm_gem_object_unreference_unlocked(obj);
 }

 /**
@@ -329,6 +334,8 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
        int ret;

        WARN_ON(!mutex_is_locked(&dev->object_name_lock));
+       if (obj->handle_count++ == 0)
+               drm_gem_object_reference(obj);

        /*
         * Get the user-visible handle using idr.  Preload and perform
@@ -338,10 +345,10 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
        spin_lock(&file_priv->table_lock);

        ret = idr_alloc(&file_priv->object_idr, obj, 1, 0, GFP_NOWAIT);
-       drm_gem_object_reference(obj);
-       obj->handle_count++;
+
        spin_unlock(&file_priv->table_lock);
        idr_preload_end();
+
        mutex_unlock(&dev->object_name_lock);
        if (ret < 0)
                goto err_unref;
-- 
2.6.4