linux-kernel - Re: [PATCH v2 0/2] Add epoll round robin wakeup mode

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Date:	Tue, 17 Feb 2015 11:46:14 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Jason Baron <jbaron@...mai.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Wong <normalperson@...t.net>,
	Davide Libenzi <davidel@...ilserver.org>,
	Michael Kerrisk-manpages <mtk.manpages@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] Add epoll round robin wakeup mode

On Tue, Feb 17, 2015 at 11:33 AM, Jason Baron <jbaron@...mai.com> wrote:
> When we are sharing a wakeup source among multiple epoll fds, we end up with
> thundering herd wakeups, since there is currently no way to add to the
> wakeup source exclusively. This series introduces 2 new epoll flags,
> EPOLLEXCLUSIVE for adding to a wakeup source exclusively. And EPOLLROUNDROBIN
> which is to be used in conjunction to EPOLLEXCLUSIVE to evenly
> distribute the wakeups. This patch was originally motivated by a desire to
> improve wakeup balance and cpu usage for a listen socket() shared amongst
> multiple epoll fd sets.
>
> See: http://lwn.net/Articles/632590/ for previous test program and testing
> resutls.
>
> Epoll manpage text:
>
> EPOLLEXCLUSIVE
>         Provides exclusive wakeups when attaching multiple epoll fds to a
>         shared wakeup source. Must be specified with an EPOLL_CTL_ADD operation.
>
> EPOLLROUNDROBIN
>         Provides balancing for exclusive wakeups when attaching multiple epoll
>         fds to a shared wakeup soruce. Depends on EPOLLEXCLUSIVE being set and
>         must be specified with an EPOLL_CTL_ADD operation.
>
> Thanks,

What permissions do you need on the file descriptor to do this?  This
will be the first case where a poll-like operation has side effects,
and that's rather weird IMO.

--Andy

>
> -Jason
>
>
> Jason Baron (2):
>   sched/wait: add round robin wakeup mode
>   epoll: introduce EPOLLEXCLUSIVE and EPOLLROUNDROBIN
>
>  fs/eventpoll.c                 | 25 ++++++++++++++++++++-----
>  include/linux/wait.h           | 11 +++++++++++
>  include/uapi/linux/eventpoll.h |  6 ++++++
>  kernel/sched/wait.c            | 10 ++++++++--
>  4 files changed, 45 insertions(+), 7 deletions(-)
>
> --
> 1.8.2.rc2
>
> --
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-- 
Andy Lutomirski
AMA Capital Management, LLC
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