From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756011AbXHCEc3 (ORCPT ); Fri, 3 Aug 2007 00:32:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751498AbXHCEcW (ORCPT ); Fri, 3 Aug 2007 00:32:22 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:38672 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751103AbXHCEcV (ORCPT ); Fri, 3 Aug 2007 00:32:21 -0400 Subject: Re: CFS review From: Arjan van de Ven To: Willy Tarreau Cc: Matt Mackall , Ingo Molnar , Roman Zippel , Mike Galbraith , Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org In-Reply-To: <20070803041808.GA6002@1wt.eu> References: <20070711214649.GK14435@v2.random> <1184302024.6709.11.camel@Homer.simpson.net> <1184389456.6632.13.camel@Homer.simpson.net> <20070801112229.GA11710@elte.hu> <20070803030436.GO11166@waste.org> <1186113467.3996.0.camel@laptopd505.fenrus.org> <20070803041808.GA6002@1wt.eu> Content-Type: text/plain Organization: Intel International BV Date: Thu, 02 Aug 2007 21:31:19 -0700 Message-Id: <1186115480.3996.2.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.10.3 (2.10.3-2.fc7) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2007-08-03 at 06:18 +0200, Willy Tarreau wrote: > On Thu, Aug 02, 2007 at 08:57:47PM -0700, Arjan van de Ven wrote: > > On Thu, 2007-08-02 at 22:04 -0500, Matt Mackall wrote: > > > On Wed, Aug 01, 2007 at 01:22:29PM +0200, Ingo Molnar wrote: > > > > > > > > * Roman Zippel 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. > > > > > > ..which is pretty much the state of play for lots of non-x86 hardware. > > > > question is if it's significantly worse than before. With a 100 or > > 1000Hz timer, you can't expect perfect fairness just due to the > > extremely rough measurement of time spent... > > Well, at least we're able to *measure* that task 'l' used 3.3% and > that tasks 'lt' used 32%. It's not measured if you use jiffies level stuff. It's at best sampled! > If we're able to measure it, then that's > already fine enough to be able to adjust future timeslices credits. > Granted it may be rough for small periods (a few jiffies), but it > should be fair for larger periods. Or at least it should *report* but the testcase here uses a LOT shorter time than jiffies... not "a few jiffies". -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org