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

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.sem...@linaro.org>
Cc: Gustavo Padovan <gust...@padovan.org>
---
 drivers/dma-buf/sync_debug.c |  3 ++-
 drivers/dma-buf/sync_file.c  | 34 +++++++++++++++++++++++++++-------
 include/linux/sync_file.h    |  5 +++--
 3 files changed, 32 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..d105079ec45c 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 +124,31 @@ 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)
+{
+       if (!sync_file->user_name[0]) {
+               scnprintf(sync_file->user_name,
+                         sizeof(sync_file->user_name),
+                         "%s-%s%llu-%d",
+                         
sync_file->fence->ops->get_driver_name(sync_file->fence),
+                         
sync_file->fence->ops->get_timeline_name(sync_file->fence),
+                         sync_file->fence->context,
+                         sync_file->fence->seqno);
+       }
+
+       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 +286,7 @@ 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 +439,7 @@ 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 */
-- 
2.11.0

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