From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH v3 0/3] epoll: introduce round robin wakeup mode Date: Fri, 27 Feb 2015 13:10:34 -0800 Message-ID: <20150227131034.2f2787dcabf285191a1f6ffa@linux-foundation.org> References: <20150225073814.GA14558@gmail.com> <54EDF7D8.60201@akamai.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <54EDF7D8.60201-JqFfY2XvxFXQT0dZR+AlfA@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jason Baron Cc: Ingo Molnar , peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@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 On Wed, 25 Feb 2015 11:27:04 -0500 Jason Baron wrote: > > 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? > > > Generally, Andrew and Al do more 'final' reviews here, > and a lot of others on lkml are always very helpful in > looking at this code. However, its not always clear, at > least to me, who I should pester. Yes, it's a difficult situation. The 3/3 changelog refers to "EPOLLROUNDROBIN" which I assume is a leftover from some earlier revision? I don't really understand the need for rotation/round-robin. We can solve the thundering herd via exclusive wakeups, but what is the point in choosing to wake the task which has been sleeping for the longest time? Why is that better than waking the task which has been sleeping for the *least* time? That's probably faster as that task's data is more likely to still be in cache. The changelogs talks about "starvation" but they don't really say what this term means in this context, nor why it is a bad thing.