From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763886AbXHAMVO (ORCPT ); Wed, 1 Aug 2007 08:21:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752650AbXHAMVB (ORCPT ); Wed, 1 Aug 2007 08:21:01 -0400 Received: from scrub.xs4all.nl ([194.109.195.176]:1862 "EHLO scrub.xs4all.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751888AbXHAMVA (ORCPT ); Wed, 1 Aug 2007 08:21:00 -0400 Date: Wed, 1 Aug 2007 14:21:21 +0200 (CEST) From: Roman Zippel X-X-Sender: roman@scrub.home To: Ingo Molnar cc: Mike Galbraith , Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: CFS review In-Reply-To: <20070801112229.GA11710@elte.hu> Message-ID: References: <20070711174252.GA16793@elte.hu> <20070711211638.GE18767@one.firstfloor.org> <20070711214649.GK14435@v2.random> <1184302024.6709.11.camel@Homer.simpson.net> <1184389456.6632.13.camel@Homer.simpson.net> <20070801112229.GA11710@elte.hu> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Wed, 1 Aug 2007, Ingo Molnar wrote: > > [...] e.g. in this example there are three tasks that run only for > > about 1ms every 3ms, but they get far more time than should have > > gotten fairly: > > > > 4544 roman 20 0 1796 520 432 S 32.1 0.4 0:21.08 lt > > 4545 roman 20 0 1796 344 256 R 32.1 0.3 0:21.07 lt > > 4546 roman 20 0 1796 344 256 R 31.7 0.3 0:21.07 lt > > 4547 roman 20 0 1532 272 216 R 3.3 0.2 0:01.94 l > > Mike and me have managed to reproduce similarly looking 'top' output, > but it takes some effort: we had to deliberately run a non-TSC > sched_clock(), CONFIG_HZ=100, !CONFIG_NO_HZ and !CONFIG_HIGH_RES_TIMERS. I used my old laptop for these tests, where tsc is indeed disabled due to instability. Otherwise the kernel was configured with CONFIG_HZ=1000. > in that case 'top' accounting symptoms similar to the above are not due > to the scheduler starvation you suspected, but due the effect of a > low-resolution scheduler clock and a tightly coupled timer/scheduler > tick to it. Well, it magnifies the rounding problems in CFS. I mainly wanted to test a little the behaviour of CFS and I thought a saw patch which enabled the use of TSC in these cases, so I didn't check sched_clock(). Anyway, I want to point out that this wasn't the main focus of what I wrote. bye, Roman