From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757449Ab3FCNP2 (ORCPT ); Mon, 3 Jun 2013 09:15:28 -0400 Received: from mail-pd0-f179.google.com ([209.85.192.179]:42007 "EHLO mail-pd0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751903Ab3FCNP0 (ORCPT ); Mon, 3 Jun 2013 09:15:26 -0400 Message-ID: <1370265324.24311.136.camel@edumazet-glaptop> Subject: Re: [PATCH v8 net-next 5/7] net: simple poll/select low latency socket poll From: Eric Dumazet To: Eliezer Tamir Cc: David Miller , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Jesse Brandeburg , Don Skidmore , e1000-devel@lists.sourceforge.net, Willem de Bruijn , Ben Hutchings , Andi Kleen , HPA , Eilon Greenstien , Or Gerlitz , Alex Rosenbaum , Eliezer Tamir Date: Mon, 03 Jun 2013 06:15:24 -0700 In-Reply-To: <20130603080200.18273.52073.stgit@ladj378.jer.intel.com> References: <20130603080107.18273.34279.stgit@ladj378.jer.intel.com> <20130603080200.18273.52073.stgit@ladj378.jer.intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2013-06-03 at 11:02 +0300, Eliezer Tamir wrote: > A very naive select/poll busy-poll support. > Add busy-polling to sock_poll(). > When poll/select have nothing to report, call the low-level > sock_poll() again untill we are out of time or we find something. > Rigth now we poll every socket once, this is subpotimal > but impoves latency when the number of sockets polled is not large. > > Signed-off-by: Alexander Duyck > Signed-off-by: Jesse Brandeburg > Tested-by: Willem de Bruijn > Signed-off-by: Eliezer Tamir > --- > > fs/select.c | 7 +++++++ > net/socket.c | 10 +++++++++- > 2 files changed, 16 insertions(+), 1 deletions(-) > > diff --git a/fs/select.c b/fs/select.c > index 8c1c96c..f116bf0 100644 > --- a/fs/select.c > +++ b/fs/select.c > @@ -27,6 +27,7 @@ > #include > #include > #include > +#include > > #include > > @@ -400,6 +401,7 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time) > poll_table *wait; > int retval, i, timed_out = 0; > unsigned long slack = 0; > + cycles_t ll_time = ll_end_time(); > > rcu_read_lock(); > retval = max_select_fd(n, fds); > @@ -486,6 +488,8 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time) > break; > } > > + if (can_poll_ll(ll_time)) > + continue; > /* > * If this is the first loop and we have a timeout > * given, then we convert to ktime_t and set the to > @@ -750,6 +754,7 @@ static int do_poll(unsigned int nfds, struct poll_list *list, > ktime_t expire, *to = NULL; > int timed_out = 0, count = 0; > unsigned long slack = 0; > + cycles_t ll_time = ll_end_time(); > > /* Optimise the no-wait case */ > if (end_time && !end_time->tv_sec && !end_time->tv_nsec) { > @@ -795,6 +800,8 @@ static int do_poll(unsigned int nfds, struct poll_list *list, > if (count || timed_out) > break; > > + if (can_poll_ll(ll_time)) > + continue; > /* > * If this is the first loop and we have a timeout > * given, then we convert to ktime_t and set the to > diff --git a/net/socket.c b/net/socket.c > index 721f4e7..02d0e15 100644 > --- a/net/socket.c > +++ b/net/socket.c > @@ -1148,13 +1148,21 @@ EXPORT_SYMBOL(sock_create_lite); > /* No kernel lock held - perfect */ > static unsigned int sock_poll(struct file *file, poll_table *wait) > { > + unsigned int poll_result; > struct socket *sock; > > /* > * We can't return errors to poll, so it's either yes or no. > */ > sock = file->private_data; > - return sock->ops->poll(file, sock, wait); > + > + poll_result = sock->ops->poll(file, sock, wait); > + > + if (!(poll_result & (POLLRDNORM | POLLERR | POLLRDHUP | POLLHUP)) && > + sk_valid_ll(sock->sk) && sk_poll_ll(sock->sk, 1)) > + poll_result = sock->ops->poll(file, sock, NULL); > + > + return poll_result; > } > > static int sock_mmap(struct file *file, struct vm_area_struct *vma) > In fact, for TCP, POLLOUT event being ready can also be triggered by incoming messages, as the ACK might allow the user application to push more data in the write queue. And you might check wait->_key to avoid testing flags that user is not interested into.