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
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---
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);
