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Registered in England and Wales under Company Registration No. 3798903 Subject: [RFC PATCH 11/11] pipe: Increase the writer-wakeup threshold to reduce context-switch count [ver #3] From: David Howells To: torvalds@linux-foundation.org Cc: dhowells@redhat.com, Rasmus Villemoes , Greg Kroah-Hartman , Peter Zijlstra , nicolas.dichtel@6wind.com, raven@themaw.net, Christian Brauner , dhowells@redhat.com, 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-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 01 Nov 2019 17:35:41 +0000 Message-ID: <157262974145.13142.5910403713310791673.stgit@warthog.procyon.org.uk> In-Reply-To: <157262963995.13142.5568934007158044624.stgit@warthog.procyon.org.uk> References: <157262963995.13142.5568934007158044624.stgit@warthog.procyon.org.uk> User-Agent: StGit/unknown-version MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-MC-Unique: jObNGFxmMiqYnw6I3pTN-A-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: 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 Signed-off-by: David Howells --- 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) =09=09=09} =20 =09=09=09if (!buf->len) { +=09=09=09=09bool wake; =09=09=09=09pipe_buf_release(pipe, buf); =09=09=09=09spin_lock_irq(&pipe->wait.lock); =09=09=09=09tail++; =09=09=09=09pipe->tail =3D tail; =09=09=09=09do_wakeup =3D 1; -=09=09=09=09if (head - (tail - 1) =3D=3D pipe->max_usage) +=09=09=09=09wake =3D head - (tail - 1) =3D=3D pipe->max_usage / 2; +=09=09=09=09if (wake) =09=09=09=09=09wake_up_interruptible_sync_poll_locked( =09=09=09=09=09=09&pipe->wait, EPOLLOUT | EPOLLWRNORM); =09=09=09=09spin_unlock_irq(&pipe->wait.lock); -=09=09=09=09if (head - (tail - 1) =3D=3D pipe->max_usage) +=09=09=09=09if (wake) =09=09=09=09=09kill_fasync(&pipe->fasync_writers, SIGIO, POLL_OUT); =09=09=09} =09=09=09total_len -=3D chars;