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Date: Fri, 13 Jan 2023 10:32:19 +0100
From: Sedat Dilek <sedat.dilek@...il.com>
To: Hongchen Zhang <zhanghongchen@...ngson.cn>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
David Howells <dhowells@...hat.com>,
Matthew Wilcox <willy@...radead.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
"Christian Brauner (Microsoft)" <brauner@...nel.org>,
Luis Chamberlain <mcgrof@...nel.org>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
"Fabio M. De Francesco" <fmdefrancesco@...il.com>,
Christophe JAILLET <christophe.jaillet@...adoo.fr>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] pipe: use __pipe_{lock,unlock} instead of spinlock
On Fri, Jan 13, 2023 at 4:19 AM Hongchen Zhang
<zhanghongchen@...ngson.cn> wrote:
>
> Hi All,
> any question about this patch, can it be merged?
>
> Thanks
> On 2023/1/7 am 9:23, Hongchen Zhang wrote:
> > Use spinlock in pipe_read/write cost too much time,IMO
> > 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.
> >
> > Reminded by Matthew, 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.
> >
> > Reminded by Andrew, I tested this patch with the test code in
> > Linus's 0ddad21d3e99 add get following result:
Happy new 2023 Hongchen Zhang,
Thanks for the update and sorry for the late response.
Should be "...s/add/and get following result:"
I cannot say much about the patch itself or tested it in my build-environment.
Best regards,
-Sedat-
> > 1) before this patch
> > 13,136.54 msec task-clock # 3.870 CPUs utilized
> > 1,186,779 context-switches # 90.342 K/sec
> > 668,867 cpu-migrations # 50.917 K/sec
> > 895 page-faults # 68.131 /sec
> > 29,875,711,543 cycles # 2.274 GHz
> > 12,372,397,462 instructions # 0.41 insn per cycle
> > 2,480,235,723 branches # 188.804 M/sec
> > 47,191,943 branch-misses # 1.90% of all branches
> >
> > 3.394806886 seconds time elapsed
> >
> > 0.037869000 seconds user
> > 0.189346000 seconds sys
> >
> > 2) after this patch
> >
> > 12,395.63 msec task-clock # 4.138 CPUs utilized
> > 1,193,381 context-switches # 96.274 K/sec
> > 585,543 cpu-migrations # 47.238 K/sec
> > 1,063 page-faults # 85.756 /sec
> > 27,691,587,226 cycles # 2.234 GHz
> > 11,738,307,999 instructions # 0.42 insn per cycle
> > 2,351,299,522 branches # 189.688 M/sec
> > 45,404,526 branch-misses # 1.93% of all branches
> >
> > 2.995280878 seconds time elapsed
> >
> > 0.010615000 seconds user
> > 0.206999000 seconds sys
> > After adding this patch, the time used on this test program becomes less.
> >
> > Signed-off-by: Hongchen Zhang <zhanghongchen@...ngson.cn>
> >
> > v3:
> > - fixes the error reported by kernel test robot <oliver.sang@...el.com>
> > Link: https://lore.kernel.org/oe-lkp/202301061340.c954d61f-oliver.sang@intel.com
> > - add perf stat data for the test code in Linus's 0ddad21d3e99 in
> > commit message.
> > v2:
> > - add UnixBench test data in commit message
> > - fixes the test error reported by kernel test robot <lkp@...el.com>
> > by adding the missing fs.h header file.
> > ---
> > fs/pipe.c | 22 +---------------------
> > include/linux/pipe_fs_i.h | 12 ++++++++++++
> > kernel/watch_queue.c | 8 ++++----
> > 3 files changed, 17 insertions(+), 25 deletions(-)
> >
> > diff --git a/fs/pipe.c b/fs/pipe.c
> > index 42c7ff41c2db..4355ee5f754e 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 +1244,12 @@ 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);
> > 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);
> > kfree(bufs);
> > return -EBUSY;
> > }
> > @@ -1303,8 +1285,6 @@ 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);
> > -
> > /* This might have made more room for writers */
> > wake_up_interruptible(&pipe->wr_wait);
> > return 0;
> > 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
> >
>
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