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Date: Wed, 4 Jan 2023 11:46:27 +0800
From: Hongchen Zhang <zhanghongchen@...ngson.cn>
To: Matthew Wilcox <willy@...radead.org>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Kuniyuki Iwashima <kuniyu@...zon.co.jp>,
Luis Chamberlain <mcgrof@...nel.org>,
David Howells <dhowells@...hat.com>,
Christophe JAILLET <christophe.jaillet@...adoo.fr>,
Randy Dunlap <rdunlap@...radead.org>,
Eric Dumazet <edumazet@...gle.com>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] pipe: use __pipe_{lock,unlock} instead of spinlock
Hi Matthew,
On 2023/1/4 am 1:51, Matthew Wilcox wrote:
> 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?
>
I tested this patch using UnixBench's pipe test case on a x86_64
machine,and get the following data:
1) before this patch
System Benchmarks Partial Index BASELINE RESULT INDEX
Pipe Throughput 12440.0 493023.3 396.3
========
System Benchmarks Index Score (Partial Only) 396.3
2) after this patch
System Benchmarks Partial Index BASELINE RESULT INDEX
Pipe Throughput 12440.0 507551.4 408.0
========
System Benchmarks Index Score (Partial Only) 408.0
so we get ~3% speedup.
>> 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@...ngson.cn>
>> ---
>
> you're supposed to write here what changes you made between v1 and v2.
>
I added the linux/fs.h in v2 to fix the linux-test-robot test error in v1.
>> 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
>>
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