[PATCH] pipe: remove needless spin_lock in pipe_read/pipe_write

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Once enable CONFIG_WATCH_QUEUE, we should protect pipe with
pipe->rd_wait.lock since post_one_notification may write pipe from
contexts where pipe->mutex cannot be token. But nowdays we will try
take it for anycase, it seems needless. Besides, pipe_write will break
once it's pipe with O_NOTIFICATION_PIPE, pipe->rd_wait.lock seems no
need at all. We make some change base on that, and it can help improve
performance for some case like pipe_pst1 in libMicro.

ARMv7 for our scene, before this patch:
  5483 nsecs/call
After this patch:
  4854 nsecs/call

Signed-off-by: yangerkun <yangerkun@xxxxxxxxxx>
---
 fs/pipe.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 6d4342bad9f1..e8ced0c50824 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -320,14 +320,18 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
 
 			if (!buf->len) {
 				pipe_buf_release(pipe, buf);
-				spin_lock_irq(&pipe->rd_wait.lock);
 #ifdef CONFIG_WATCH_QUEUE
+				if (pipe->watch_queue)
+					spin_lock_irq(&pipe->rd_wait.lock);
 				if (buf->flags & PIPE_BUF_FLAG_LOSS)
 					pipe->note_loss = true;
 #endif
 				tail++;
 				pipe->tail = tail;
-				spin_unlock_irq(&pipe->rd_wait.lock);
+#ifdef CONFIG_WATCH_QUEUE
+				if (pipe->watch_queue)
+					spin_unlock_irq(&pipe->rd_wait.lock);
+#endif
 			}
 			total_len -= chars;
 			if (!total_len)
@@ -504,16 +508,11 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 			 * it, either the reader will consume it or it'll still
 			 * be there for the next write.
 			 */
-			spin_lock_irq(&pipe->rd_wait.lock);
-
 			head = pipe->head;
-			if (pipe_full(head, pipe->tail, pipe->max_usage)) {
-				spin_unlock_irq(&pipe->rd_wait.lock);
+			if (pipe_full(head, pipe->tail, pipe->max_usage))
 				continue;
-			}
 
 			pipe->head = head + 1;
-			spin_unlock_irq(&pipe->rd_wait.lock);
 
 			/* Insert it into the buffer array */
 			buf = &pipe->bufs[head & mask];
-- 
2.31.1




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