On Tue, Jul 12, 2016 at 10:46:45AM +0200, Maarten Lankhorst wrote:
Op 11-07-16 om 22:27 schreef Gustavo Padovan:
2016-07-10 Maarten Lankhorst maarten.lankhorst@linux.intel.com:
Op 08-07-16 om 17:44 schreef Gustavo Padovan:
From: Gustavo Padovan gustavo.padovan@collabora.co.uk
Signalling doesn't need to be enabled at sync_file creation, it is only required if userspace waiting the fence to signal through poll().
Thus we delay fence_add_callback() until poll is called. It only adds the callback the first time poll() is called. This avoid re-adding the same callback multiple times.
v2: rebase and update to work with new fence support for sync_file
Signed-off-by: Gustavo Padovan gustavo.padovan@collabora.co.uk
This patch applies on top of my latest sync_file changes to support fence_array: https://lkml.org/lkml/2016/7/4/534
drivers/dma-buf/sync_file.c | 23 ++++++++++++++--------- include/linux/sync_file.h | 2 ++ 2 files changed, 16 insertions(+), 9 deletions(-)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c index 61a687c..1db4a64 100644 --- a/drivers/dma-buf/sync_file.c +++ b/drivers/dma-buf/sync_file.c @@ -86,8 +86,6 @@ struct sync_file *sync_file_create(struct fence *fence) fence->ops->get_timeline_name(fence), fence->context, fence->seqno);
- fence_add_callback(fence, &sync_file->cb, fence_check_cb_func);
- return sync_file;
} EXPORT_SYMBOL(sync_file_create); @@ -269,9 +267,6 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a, goto err; }
- fence_add_callback(sync_file->fence, &sync_file->cb,
fence_check_cb_func);- strlcpy(sync_file->name, name, sizeof(sync_file->name)); return sync_file;
@@ -286,7 +281,6 @@ static void sync_file_free(struct kref *kref) struct sync_file *sync_file = container_of(kref, struct sync_file, kref);
- fence_remove_callback(sync_file->fence, &sync_file->cb); fence_put(sync_file->fence); kfree(sync_file);
} @@ -306,13 +300,24 @@ static unsigned int sync_file_poll(struct file *file, poll_table *wait)
poll_wait(file, &sync_file->wq, wait);
- if (!sync_file->enabled) {
fence_add_callback(sync_file->fence, &sync_file->cb,fence_check_cb_func);sync_file->enabled = true;- }
Won't this blow up completely with 2 threads polling at the same time?
Indeed, using atomic operations on enabled should fix this.
No, it still would blow up without locking around fence_remove/add_callback too..
Personally I would just add the callback once, then remove it in destructor.
Something like:
poll: if (!atomic_xchg(&sync_file->enabled, 1)) { if (fence_add_callback(...) < 0) wake up sync_file->wq, fence is signaled }
sync_file_free: if (atomic_read(&sync_file->enabled)) fence_remove_callback(...);
fence_put()
It's not like fence can disable hw signaling when all callbacks are removed anyway, it's harmless to keep it on the list.
+1 from me on this plan, removing the callbacks doesn't provide any value (before the sync_file is destroyed). Also, when someone polls, you can expect to get repolled a lot until the fences finally all signal. -Daniel