From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763574AbXHAOhJ (ORCPT ); Wed, 1 Aug 2007 10:37:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763874AbXHAOgq (ORCPT ); Wed, 1 Aug 2007 10:36:46 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:44534 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763093AbXHAOgo (ORCPT ); Wed, 1 Aug 2007 10:36:44 -0400 Date: Wed, 1 Aug 2007 16:36:24 +0200 From: Ingo Molnar To: Roman Zippel Cc: Andi Kleen , Mike Galbraith , Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: CFS review Message-ID: <20070801143624.GA18043@elte.hu> References: <20070711211638.GE18767@one.firstfloor.org> <20070711214649.GK14435@v2.random> <1184302024.6709.11.camel@Homer.simpson.net> <1184389456.6632.13.camel@Homer.simpson.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: 1.0 X-ELTE-SpamLevel: s X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=1.0 required=5.9 tests=BAYES_50 autolearn=no SpamAssassin version=3.0.3 1.0 BAYES_50 BODY: Bayesian spam probability is 40 to 60% [score: 0.5000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Roman Zippel wrote: > > jiffies based sched_clock should be soon very rare. It's probably > > not worth optimizing for it. > > I'm not so sure about that. sched_clock() has to be fast, so many > archs may want to continue to use jiffies. [...] i think Andi was talking about the vast majority of the systems out there. For example, check out the arch demography of current Fedora installs (according to the Smolt opt-in UUID based user metrics): http://smolt.fedoraproject.org/ i686: 74743 x86_64: 18599 i386: 1208 ppc: 527 ppc64: 396 sparc64: 14 --------------- Total: 95488 even pure i386 (kernels, not systems) is a only 1.2% of all installs. By the time the CFS kernel gets into a distro (a few months at minimum, typically a year) this percentage will go down further. And embedded doesnt really care about task-statistics corner cases [ (it likely doesnt have 'top' installed - likely doesnt even have /proc mounted or even built in ;-) ]. of course CFS should not do _worse_ stats than what we had before, and should not break or massively misbehave. Also, anything sane we can do for low-resolution arches we should do (and we already do quite a bit - the while wmult stuff is to avoid expensive divisions) - and i regularly booted CFS with a low-resolution clock to make sure it works. So i'm not trying to duck anything, we've just got to keep our design priorities right :-) Ingo