From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752535Ab0H0ITt (ORCPT ); Fri, 27 Aug 2010 04:19:49 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:43497 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1752322Ab0H0ITr (ORCPT ); Fri, 27 Aug 2010 04:19:47 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX18YV5Nt6fAYo97gEuKZqYjLFmCIpHb6uDmwnMsDZQ y5Azi+5E/Fn7Fg Subject: Re: [RFC PATCH 00/11] sched: CFS low-latency features From: Mike Galbraith To: Peter Zijlstra Cc: Mathieu Desnoyers , LKML , Linus Torvalds , Andrew Morton , Ingo Molnar , Steven Rostedt , Thomas Gleixner , Tony Lindgren In-Reply-To: <1282894960.1975.1666.camel@laptop> References: <20100826180908.648103531@efficios.com> <1282849045.1975.1587.camel@laptop> <20100826234910.GB4194@Krystal> <1282894960.1975.1666.camel@laptop> Content-Type: text/plain Date: Fri, 27 Aug 2010 10:19:52 +0200 Message-Id: <1282897192.7185.28.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1.1 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2010-08-27 at 09:42 +0200, Peter Zijlstra wrote: > On Thu, 2010-08-26 at 19:49 -0400, Mathieu Desnoyers wrote: > > AFAIK, I don't think we would end up starving the system in any possible way. > > Correct, it does maintain fairness. > > > So far I cannot see a situation where selecting the next buddy would _not_ make > > sense in any kind of input-driven wakeups (interactive, timer, disk, network, > > etc). But maybe it's just a lack of imagination on my part. > > The risk is that you end up with always using next-buddy, and we tried > that a while back and that didn't work well for some, Mike might > remember. I turned it off because it was ripping spread apart badly, and last buddy did a better job of improving scalability without it. > Also, when you use timers things like time-outs you really couldn't care > less if its handled sooner rather than later. > > Disk is usually so slow you really don't want to consider it > interactive, but then sometimes you might,.. its a really hard problem. (very hard) > The only clear situation is the direct input, that's a direct link > between the user and our wakeup chain and the user is always important. Yeah, directly linked wakeups using next could be a good thing, but the trouble with using any linkage to the user is that you have to pass it on to reap benefit.. so when do you disconnect? -Mike