From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: David Howells <dhowells@redhat.com>
Cc: torvalds@linux-foundation.org,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Zijlstra <peterz@infradead.org>,
nicolas.dichtel@6wind.com, raven@themaw.net,
Christian Brauner <christian@brauner.io>,
keyrings@vger.kernel.org, linux-usb@vger.kernel.org,
linux-block@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 07/10] pipe: Conditionalise wakeup in pipe_read() [ver #2]
Date: Sun, 3 Nov 2019 14:04:23 +0300 [thread overview]
Message-ID: <f8810057-d92a-bcd2-c703-0a947336ce8d@yandex-team.ru> (raw)
In-Reply-To: <3165.1572539884@warthog.procyon.org.uk>
On 31/10/2019 19.38, David Howells wrote:
> Okay, attached is a change that might give you what you want. I tried my
> pipe-bench program (see cover note) with perf. The output of the program with
> the patch applied was:
>
> - pipe 305127298 36262221772 302185181 7887690
>
> The output of perf with the patch applied:
>
> 239,943.92 msec task-clock # 1.997 CPUs utilized
> 17,728 context-switches # 73.884 M/sec
> 124 cpu-migrations # 0.517 M/sec
> 9,330 page-faults # 38.884 M/sec
> 885,107,207,365 cycles # 3688822.793 GHz
> 1,386,873,499,490 instructions # 1.57 insn per cycle
> 311,037,372,339 branches # 1296296921.931 M/sec
> 33,467,827 branch-misses # 0.01% of all branches
>
> And without:
>
> 239,891.87 msec task-clock # 1.997 CPUs utilized
> 22,187 context-switches # 92.488 M/sec
> 133 cpu-migrations # 0.554 M/sec
> 9,334 page-faults # 38.909 M/sec
> 884,906,976,128 cycles # 3688787.725 GHz
> 1,391,986,932,265 instructions # 1.57 insn per cycle
> 311,394,686,857 branches # 1298067400.849 M/sec
> 30,242,823 branch-misses # 0.01% of all branches
>
> So it did make something like a 20% reduction in context switches.
Ok. Looks promising. Depending on workload reduction might be much bigger.
I suppose buffer resize (grow) makes wakeup unconditionally. Should be ok.
>
> David
> ---
> diff --git a/fs/pipe.c b/fs/pipe.c
> index e3d5f7a39123..5167921edd73 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -276,7 +276,7 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
> size_t total_len = iov_iter_count(to);
> struct file *filp = iocb->ki_filp;
> struct pipe_inode_info *pipe = filp->private_data;
> - int do_wakeup;
> + int do_wakeup, wake;
> ssize_t ret;
>
> /* Null read succeeds. */
> @@ -329,11 +329,12 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
> tail++;
> pipe->tail = tail;
> do_wakeup = 1;
> - if (head - (tail - 1) == pipe->max_usage)
> + wake = head - (tail - 1) == pipe->max_usage / 2;
> + if (wake)
> wake_up_interruptible_sync_poll_locked(
> &pipe->wait, EPOLLOUT | EPOLLWRNORM);
> spin_unlock_irq(&pipe->wait.lock);
> - if (head - (tail - 1) == pipe->max_usage)
> + if (wake)
> kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT);
> }
> total_len -= chars;
>
next prev parent reply other threads:[~2019-11-03 11:04 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-23 20:17 [RFC PATCH 00/10] pipe: Notification queue preparation [ver #2] David Howells
2019-10-23 20:17 ` [RFC PATCH 01/10] pipe: Reduce #inclusion of pipe_fs_i.h " David Howells
2019-10-23 20:17 ` [RFC PATCH 02/10] Remove the nr_exclusive argument from __wake_up_sync_key() " David Howells
2019-10-23 20:17 ` [RFC PATCH 03/10] Add wake_up_interruptible_sync_poll_locked() " David Howells
2019-10-23 20:17 ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length " David Howells
2019-10-26 14:58 ` [pipe] 6567a02d20: BUG:kernel_NULL_pointer_dereference,address kernel test robot
2019-10-27 14:03 ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length [ver #2] Linus Torvalds
2019-10-30 16:19 ` Ilya Dryomov
2019-10-30 20:35 ` Rasmus Villemoes
2019-10-30 22:16 ` Ilya Dryomov
2019-10-30 22:38 ` Rasmus Villemoes
2019-10-31 15:11 ` David Howells
2019-10-31 15:57 ` Ilya Dryomov
2019-11-01 14:53 ` David Howells
2019-10-31 14:57 ` David Howells
2019-11-03 11:17 ` Matthew Wilcox
2019-12-06 21:47 ` Johannes Hirte
2019-12-06 22:14 ` Linus Torvalds
2019-12-07 0:00 ` Johannes Hirte
2019-12-07 1:03 ` Linus Torvalds
2019-12-08 17:56 ` Johannes Hirte
2019-12-08 18:10 ` Linus Torvalds
2019-12-07 6:47 ` Linus Torvalds
2019-12-06 22:15 ` David Howells
2019-10-23 20:17 ` [RFC PATCH 05/10] pipe: Allow pipes to have kernel-reserved slots " David Howells
2019-10-23 20:18 ` [RFC PATCH 06/10] pipe: Advance tail pointer inside of wait spinlock in pipe_read() " David Howells
2019-10-23 20:18 ` [RFC PATCH 07/10] pipe: Conditionalise wakeup " David Howells
2019-10-27 15:57 ` Konstantin Khlebnikov
2019-10-31 15:21 ` David Howells
2019-10-31 16:38 ` David Howells
2019-11-03 11:04 ` Konstantin Khlebnikov [this message]
2019-10-23 20:18 ` [RFC PATCH 08/10] pipe: Rearrange sequence in pipe_write() to preallocate slot " David Howells
2019-10-23 20:18 ` [RFC PATCH 09/10] pipe: Remove redundant wakeup from pipe_write() " David Howells
2019-10-23 20:18 ` [RFC PATCH 10/10] pipe: Check for ring full inside of the spinlock in " David Howells
2019-10-24 10:32 ` [RFC PATCH 04/10] pipe: Use head and tail pointers for the ring, not cursor and length " David Howells
2019-10-24 13:14 ` [RFC PATCH 00/10] pipe: Notification queue preparation " Peter Zijlstra
2019-10-24 16:57 ` [RFC PATCH 11/10] pipe: Add fsync() support " David Howells
2019-10-24 21:29 ` Linus Torvalds
2019-10-25 8:34 ` David Howells
2019-10-27 15:22 ` Christoph Hellwig
2019-10-27 16:04 ` Konstantin Khlebnikov
2019-10-31 15:13 ` David Howells
2019-10-31 15:15 ` David Howells
2019-11-02 18:53 ` Linus Torvalds
2019-11-02 19:34 ` David Howells
2019-11-02 20:31 ` Andy Lutomirski
2019-11-02 22:03 ` Linus Torvalds
2019-11-02 22:09 ` Linus Torvalds
2019-11-02 22:30 ` Andy Lutomirski
2019-11-02 23:02 ` Linus Torvalds
2019-11-02 23:09 ` Linus Torvalds
2019-11-02 23:14 ` Andy Lutomirski
2019-11-03 12:02 ` Konstantin Khlebnikov
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