From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753003AbbBYHiW (ORCPT ); Wed, 25 Feb 2015 02:38:22 -0500 Received: from mail-wi0-f182.google.com ([209.85.212.182]:37894 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750764AbbBYHiT (ORCPT ); Wed, 25 Feb 2015 02:38:19 -0500 Date: Wed, 25 Feb 2015 08:38:14 +0100 From: Ingo Molnar To: Jason Baron Cc: peterz@infradead.org, mingo@redhat.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, normalperson@yhbt.net, davidel@xmailserver.org, mtk.manpages@gmail.com, luto@amacapital.net, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, Linus Torvalds , Alexander Viro Subject: Re: [PATCH v3 0/3] epoll: introduce round robin wakeup mode Message-ID: <20150225073814.GA14558@gmail.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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