From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH v3 0/3] epoll: introduce round robin wakeup mode Date: Wed, 25 Feb 2015 08:38:14 +0100 Message-ID: <20150225073814.GA14558@gmail.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jason Baron Cc: peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org, akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, normalperson-rMlxZR9MS24@public.gmane.org, davidel-AhlLAIvw+VEjIGhXcJzhZg@public.gmane.org, mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linus Torvalds , Alexander Viro List-Id: linux-api@vger.kernel.org * Jason Baron wrote: > Hi, > > 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 a new EPOLL_ROTATE > flag to allow for round robin exclusive wakeups. > > I believe this patch series addresses the two main > concerns that were raised in prior postings. Namely, that > it affected code (and potentially performance) of the > core kernel wakeup functions, even in cases where it was > not strictly needed, and that it could lead to wakeup > starvation (since we were are no longer waking up all > waiters). It does so by adding an extra layer of > indirection, whereby waiters are attached to a 'psuedo' > epoll fd, which in turn is attached directly to the > wakeup source. > sched/wait: add __wake_up_rotate() > include/linux/wait.h | 1 + > kernel/sched/wait.c | 27 ++++++++++++++++++++++ So the scheduler bits are looking good to me in principle, because they just add a new round-robin-rotating wakeup variant and don't disturb the others. Is there consensus on the epoll ABI changes? With Davide Libenzi inactive eventpoll appears to be without a dedicated maintainer since 2011 or so. Is there anyone who knows the code and its usages in detail and does final ABI decisions on eventpoll - Andrew, Al or Linus? Thanks, Ingo