[RFC PATCH 11/11] pipe: Increase the writer-wakeup threshold to reduce context-switch count [ver #3]
From: David Howells <dhowells@redhat.com>
Date: 2019-11-01 17:35:52
Also in:
keyrings, linux-block, linux-fsdevel, linux-security-module, linux-usb, lkml
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
Increase the threshold at which the reader sends a wake event to the writers in the queue such that the queue must be half empty before the wake is issued rather than the wake being issued when just a single slot available. This reduces the number of context switches in the tests significantly, without altering the amount of work achieved. With my pipe-bench program, there's a 20% reduction versus an unpatched kernel. Suggested-by: Konstantin Khlebnikov <redacted> Signed-off-by: David Howells <dhowells@redhat.com> --- fs/pipe.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/pipe.c b/fs/pipe.c
index aba2455caabe..9cd5cbef9552 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c@@ -324,16 +324,18 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) } if (!buf->len) { + bool wake; pipe_buf_release(pipe, buf); spin_lock_irq(&pipe->wait.lock); 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;