On Tue, Jan 03, 2023 at 02:33:03PM +0800, Hongchen Zhang wrote:
> Use spinlock in pipe_read/write cost too much time,IMO
Everybody has an opinion. Do you have data?
> pipe->{head,tail} can be protected by __pipe_{lock,unlock}.
> On the other hand, we can use __pipe_lock/unlock to protect the
> pipe->head/tail in pipe_resize_ring and post_one_notification.
>
> Signed-off-by: Hongchen Zhang <zhanghongchen@xxxxxxxxxxx>
> ---
you're supposed to write here what changes you made between v1 and v2.
> fs/pipe.c | 24 ++++--------------------
> include/linux/pipe_fs_i.h | 12 ++++++++++++
> kernel/watch_queue.c | 8 ++++----
> 3 files changed, 20 insertions(+), 24 deletions(-)
>
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 42c7ff41c2db..cf449779bf71 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -98,16 +98,6 @@ void pipe_unlock(struct pipe_inode_info *pipe)
> }
> EXPORT_SYMBOL(pipe_unlock);
>
> -static inline void __pipe_lock(struct pipe_inode_info *pipe)
> -{
> - mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
> -}
> -
> -static inline void __pipe_unlock(struct pipe_inode_info *pipe)
> -{
> - mutex_unlock(&pipe->mutex);
> -}
> -
> void pipe_double_lock(struct pipe_inode_info *pipe1,
> struct pipe_inode_info *pipe2)
> {
> @@ -253,8 +243,7 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
> */
> was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage);
> for (;;) {
> - /* Read ->head with a barrier vs post_one_notification() */
> - unsigned int head = smp_load_acquire(&pipe->head);
> + unsigned int head = pipe->head;
> unsigned int tail = pipe->tail;
> unsigned int mask = pipe->ring_size - 1;
>
> @@ -322,14 +311,12 @@ 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 (buf->flags & PIPE_BUF_FLAG_LOSS)
> pipe->note_loss = true;
> #endif
> tail++;
> pipe->tail = tail;
> - spin_unlock_irq(&pipe->rd_wait.lock);
> }
> total_len -= chars;
> if (!total_len)
> @@ -506,16 +493,13 @@ 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);
> continue;
> }
>
> pipe->head = head + 1;
> - spin_unlock_irq(&pipe->rd_wait.lock);
>
> /* Insert it into the buffer array */
> buf = &pipe->bufs[head & mask];
> @@ -1260,14 +1244,14 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
> if (unlikely(!bufs))
> return -ENOMEM;
>
> - spin_lock_irq(&pipe->rd_wait.lock);
> + __pipe_lock(pipe);
> mask = pipe->ring_size - 1;
> head = pipe->head;
> tail = pipe->tail;
>
> n = pipe_occupancy(head, tail);
> if (nr_slots < n) {
> - spin_unlock_irq(&pipe->rd_wait.lock);
> + __pipe_unlock(pipe);
> kfree(bufs);
> return -EBUSY;
> }
> @@ -1303,7 +1287,7 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
> pipe->tail = tail;
> pipe->head = head;
>
> - spin_unlock_irq(&pipe->rd_wait.lock);
> + __pipe_unlock(pipe);
>
> /* This might have made more room for writers */
> wake_up_interruptible(&pipe->wr_wait);
> diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
> index 6cb65df3e3ba..f5084daf6eaf 100644
> --- a/include/linux/pipe_fs_i.h
> +++ b/include/linux/pipe_fs_i.h
> @@ -2,6 +2,8 @@
> #ifndef _LINUX_PIPE_FS_I_H
> #define _LINUX_PIPE_FS_I_H
>
> +#include <linux/fs.h>
> +
> #define PIPE_DEF_BUFFERS 16
>
> #define PIPE_BUF_FLAG_LRU 0x01 /* page is on the LRU */
> @@ -223,6 +225,16 @@ static inline void pipe_discard_from(struct pipe_inode_info *pipe,
> #define PIPE_SIZE PAGE_SIZE
>
> /* Pipe lock and unlock operations */
> +static inline void __pipe_lock(struct pipe_inode_info *pipe)
> +{
> + mutex_lock_nested(&pipe->mutex, I_MUTEX_PARENT);
> +}
> +
> +static inline void __pipe_unlock(struct pipe_inode_info *pipe)
> +{
> + mutex_unlock(&pipe->mutex);
> +}
> +
> void pipe_lock(struct pipe_inode_info *);
> void pipe_unlock(struct pipe_inode_info *);
> void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);
> diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
> index a6f9bdd956c3..92e46cfe9419 100644
> --- a/kernel/watch_queue.c
> +++ b/kernel/watch_queue.c
> @@ -108,7 +108,7 @@ static bool post_one_notification(struct watch_queue *wqueue,
> if (!pipe)
> return false;
>
> - spin_lock_irq(&pipe->rd_wait.lock);
> + __pipe_lock(pipe);
>
> mask = pipe->ring_size - 1;
> head = pipe->head;
> @@ -135,17 +135,17 @@ static bool post_one_notification(struct watch_queue *wqueue,
> buf->offset = offset;
> buf->len = len;
> buf->flags = PIPE_BUF_FLAG_WHOLE;
> - smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */
> + pipe->head = head + 1;
>
> if (!test_and_clear_bit(note, wqueue->notes_bitmap)) {
> - spin_unlock_irq(&pipe->rd_wait.lock);
> + __pipe_unlock(pipe);
> BUG();
> }
> wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
> done = true;
>
> out:
> - spin_unlock_irq(&pipe->rd_wait.lock);
> + __pipe_unlock(pipe);
> if (done)
> kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
> return done;
>
> base-commit: c8451c141e07a8d05693f6c8d0e418fbb4b68bb7
> --
> 2.31.1
>
