2017-05-22 Daniel Vetter <daniel@xxxxxxxx>:
> On Tue, May 16, 2017 at 12:10:42PM +0100, Chris Wilson wrote:
> > 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.
> > v5: Completely avoid the read/write race by only storing the name passed
> > in from the user inside sync_file->user_name and passing in a buffer to
> > dynamically construct the name otherwise.
> >
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> > Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > Cc: David Herrmann <dh.herrmann@xxxxxxxxx>
> > ---
> > drivers/dma-buf/sync_debug.c | 4 +++-
> > drivers/dma-buf/sync_file.c | 39 ++++++++++++++++++++++++++++++++-------
> > include/linux/sync_file.h | 5 +++--
> > 3 files changed, 38 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c
> > index 4b1731ee7458..59a3b2f8ee91 100644
> > --- a/drivers/dma-buf/sync_debug.c
> > +++ b/drivers/dma-buf/sync_debug.c
> > @@ -132,9 +132,11 @@ static void sync_print_obj(struct seq_file *s, struct sync_timeline *obj)
> > static void sync_print_sync_file(struct seq_file *s,
> > struct sync_file *sync_file)
> > {
> > + char buf[128];
> > 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, buf, sizeof(buf)),
> > 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..d7e219d2669d 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 +124,36 @@ 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
> > + * @buf: destination buffer to copy sync_file name into
> > + * @len: available size of destination buffer.
> > + *
> > + * Each sync_file may have a name assigned either by the user (when merging
> > + * sync_files together) or created from the fence it contains. In the latter
> > + * case construction of the name is deferred until use, and so requires
> > + * sync_file_get_name().
> > + *
> > + * Returns: a string representing the name.
> > + */
> > +char *sync_file_get_name(struct sync_file *sync_file, char *buf, int len)
> > +{
> > + if (sync_file->user_name[0]) {
> > + strlcpy(buf, sync_file->user_name, len);
> > + } else {
> > + struct dma_fence *fence = sync_file->fence;
> > +
> > + snprintf(buf, len, "%s-%s%llu-%d",
> > + fence->ops->get_driver_name(fence),
> > + fence->ops->get_timeline_name(fence),
> > + fence->context,
> > + fence->seqno);
> > + }
> > +
> > + return buf;
> > +}
> > +
> > static int sync_file_set_fence(struct sync_file *sync_file,
> > struct dma_fence **fences, int num_fences)
> > {
> > @@ -266,7 +291,7 @@ 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 +444,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> > }
> >
> > no_fences:
> > - strlcpy(info.name, sync_file->name, sizeof(info.name));
> > + sync_file_get_name(sync_file, info.name, 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..5226d62ae91b 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];
>
> Maybe inline kerneldoc an explain a bit better what's going on:
>
> /**
> * @user_name:
> *
> * Name of the sync file provided by userspace, for merged fences.
> * Otherwise generated through driver callbacks (in which case the
> * entire array is 0).
> */
>
> Might be overkill, so not going to insist at all. Either way:
>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
I fixed it. Applied with the modification proposed by Daniel. Thanks for
the patch.
Gustavo
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