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@xxxxxxxxxxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
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 */
--
2.11.0
_______________________________________________
Intel-gfx mailing list
Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/intel-gfx
