From ecebca79f6976ddaddfd054d699272515869ea28 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 29 Aug 2016 19:16:13 +0100
Subject: [PATCH] dma-buf/sync-file: Avoid enable fence signaling if
poll(.timeout=0)
If we being polled with a timeout of zero, a nonblocking busy query,
we don't need to install any fence callbacks as we will not be waiting.
As we only install the callback once, the overhead comes from the atomic
bit test that also causes serialisation between threads.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Reviewed-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20160829181613.30722-1-chris@chris-wilson.co.uk
---
drivers/dma-buf/sync_file.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 486d29c1a830d..abb5fdab75fdb 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -306,7 +306,8 @@ static unsigned int sync_file_poll(struct file *file, poll_table *wait)
poll_wait(file, &sync_file->wq, wait);
- if (!test_and_set_bit(POLL_ENABLED, &sync_file->fence->flags)) {
+ if (!poll_does_not_wait(wait) &&
+ !test_and_set_bit(POLL_ENABLED, &sync_file->fence->flags)) {
if (fence_add_callback(sync_file->fence, &sync_file->cb,
fence_check_cb_func) < 0)
wake_up_all(&sync_file->wq);
--
2.30.2