Re: [RFC PATCH 07/10] pipe: Conditionalise wakeup in pipe_read() [ver #2]
From: Konstantin Khlebnikov <hidden>
Date: 2019-10-27 15:57:48
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On 23/10/2019 23.18, David Howells wrote:
Only do a wakeup in pipe_read() if we made space in a completely full buffer. The producer shouldn't be waiting on pipe->wait otherwise.
We could go further and wakeup writer only when at least half of buffer is empty. This gives better batching and reduces rate of context switches. https://lore.kernel.org/lkml/157219118016.7078.16223055699799396042.stgit@buzz/T/#u (local)
quoted hunk ↗ jump to hunk
Signed-off-by: David Howells <dhowells@redhat.com> --- fs/pipe.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-)diff --git a/fs/pipe.c b/fs/pipe.c index 1274305772fb..e3a8f10750c9 100644 --- a/fs/pipe.c +++ b/fs/pipe.c@@ -327,11 +327,13 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) spin_lock_irq(&pipe->wait.lock); tail++; pipe_commit_read(pipe, tail); - do_wakeup = 0; - wake_up_interruptible_sync_poll_locked( - &pipe->wait, EPOLLOUT | EPOLLWRNORM); + do_wakeup = 1; + if (head - (tail - 1) == pipe->max_usage) + wake_up_interruptible_sync_poll_locked( + &pipe->wait, EPOLLOUT | EPOLLWRNORM); spin_unlock_irq(&pipe->wait.lock); - kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT); + if (head - (tail - 1) == pipe->max_usage) + kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT); } total_len -= chars; if (!total_len)@@ -360,11 +362,6 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) ret = -ERESTARTSYS; break; } - if (do_wakeup) { - wake_up_interruptible_sync_poll(&pipe->wait, EPOLLOUT | EPOLLWRNORM); - kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT); - do_wakeup = 0; - } pipe_wait(pipe); } __pipe_unlock(pipe);