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

[yangerkun <yangerkun@huawei.com>]

ping

On 2021/11/22 12:11, yangerkun wrote:
> 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@huawei.com>
> ---
>   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];
>