Constructing the name takes the majority of the time for allocating a sync_file to wrap a fence, and the name is very rarely used (only via the sync_file status user interface). To reduce the impact on the common path (that of creating sync_file to pass around), defer the construction of the name until it is first used.
v2: Update kerneldoc (kbuild test robot) v3: sync_debug.c was peeking at the name v4: Comment upon the potential race between two users of sync_file_get_name() and claim that such a race is below the level of notice. However, to prevent any future nuisance, use a global spinlock to serialize the assignment of the name.
Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Gustavo Padovan gustavo@padovan.org Cc: Daniel Vetter daniel.vetter@ffwll.ch --- drivers/dma-buf/sync_debug.c | 3 ++- drivers/dma-buf/sync_file.c | 54 ++++++++++++++++++++++++++++++++++++++------ include/linux/sync_file.h | 5 ++-- 3 files changed, 52 insertions(+), 10 deletions(-)
diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c index 4b1731ee7458..9a93f1085c63 100644 --- a/drivers/dma-buf/sync_debug.c +++ b/drivers/dma-buf/sync_debug.c @@ -134,7 +134,8 @@ static void sync_print_sync_file(struct seq_file *s, { int i;
- seq_printf(s, "[%p] %s: %s\n", sync_file, sync_file->name, + seq_printf(s, "[%p] %s: %s\n", sync_file, + sync_file_get_name(sync_file), sync_status_str(dma_fence_get_status(sync_file->fence)));
if (dma_fence_is_array(sync_file->fence)) { diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index c9eb4997cfcc..0d54de79ba76 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -80,11 +80,6 @@ struct sync_file *sync_file_create(struct dma_fence *fence)
sync_file->fence = dma_fence_get(fence);
- snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d", - fence->ops->get_driver_name(fence), - fence->ops->get_timeline_name(fence), fence->context, - fence->seqno); - return sync_file; } EXPORT_SYMBOL(sync_file_create); @@ -129,6 +124,51 @@ struct dma_fence *sync_file_get_fence(int fd) } EXPORT_SYMBOL(sync_file_get_fence);
+/** + * sync_file_get_name - get the name of the sync_file + * @sync_file: sync_file to get the fence from + * + * Each sync_file may have a name assigned either by the user (when merging + * sync_files together) or created from the fence it contains. However, + * construction of the name is deferred until first use. + * + * Returns: a string representing the name + */ +char *sync_file_get_name(struct sync_file *sync_file) +{ + static DEFINE_SPINLOCK(name_lock); + + if (!sync_file->user_name[0]) { + char buf[sizeof(sync_file->user_name)]; + struct dma_fence *fence; + int len; + + rcu_read_lock(); + fence = sync_file->fence; + len = scnprintf(buf, sizeof(buf), "%s-%s%llu-%d", + fence->ops->get_driver_name(sync_file->fence), + fence->ops->get_timeline_name(sync_file->fence), + fence->context, + fence->seqno); + + /* This is mildly racy, so we stage the printf into a local + * buffer and do the copy with preempt disabled to trim the + * race down to a few cycles. To completely eliminate the + * race, we do the final assignment underneath a global + * spinlock. A global lock should be adequate here for this + * rare path (called from the middle of a user sw_sync status + * ioctl and from debugfs). + */ + spin_lock(&name_lock); + if (!sync_file->user_name[0]) + memcpy(sync_file->user_name, buf, len + 1); + spin_unlock(&name_lock); + rcu_read_unlock(); + } + + return sync_file->user_name; +} + static int sync_file_set_fence(struct sync_file *sync_file, struct dma_fence **fences, int num_fences) { @@ -266,7 +306,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a, goto err; }
- strlcpy(sync_file->name, name, sizeof(sync_file->name)); + strlcpy(sync_file->user_name, name, sizeof(sync_file->user_name)); return sync_file;
err: @@ -419,7 +459,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file, }
no_fences: - strlcpy(info.name, sync_file->name, sizeof(info.name)); + strlcpy(info.name, sync_file_get_name(sync_file), sizeof(info.name)); info.status = dma_fence_is_signaled(sync_file->fence); info.num_fences = num_fences;
diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h index d37beefdfbd5..0f3f05325c84 100644 --- a/include/linux/sync_file.h +++ b/include/linux/sync_file.h @@ -23,7 +23,7 @@ /** * struct sync_file - sync file to export to the userspace * @file: file representing this fence - * @name: name of sync_file. Useful for debugging + * @user_name: name of sync_file. Useful for debugging * @sync_file_list: membership in global file list * @wq: wait queue for fence signaling * @fence: fence with the fences in the sync_file @@ -31,7 +31,7 @@ */ struct sync_file { struct file *file; - char name[32]; + char user_name[32]; #ifdef CONFIG_DEBUG_FS struct list_head sync_file_list; #endif @@ -46,5 +46,6 @@ struct sync_file {
struct sync_file *sync_file_create(struct dma_fence *fence); struct dma_fence *sync_file_get_fence(int fd); +char *sync_file_get_name(struct sync_file *sync_file);
#endif /* _LINUX_SYNC_H */