Re: [PATCH v3] pipe: use __pipe_{lock,unlock} instead of spinlock
From: maobibo
Date: Sun Jan 15 2023 - 22:16:35 EST
Hongchen,
I have a glance with this patch, it simply replaces with
spinlock_irqsave with mutex lock. There may be performance
improvement with two processes competing with pipe, however
for N processes, there will be complex context switches
and ipi interruptts.
Can you find some cases with more than 2 processes competing
pipe, rather than only unixbench?
regards
bibo, mao
在 2023/1/13 11:19, Hongchen Zhang 写道:
> 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:
>> 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@xxxxxxxxxxx>
>>
>> v3:
>> - fixes the error reported by kernel test robot <oliver.sang@xxxxxxxxx>
>> Link: https://lore.kernel.org/oe-lkp/202301061340.c954d61f-oliver.sang@xxxxxxxxx
>> - 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@xxxxxxxxx>
>> 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
>>