From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758064AbXGPHl4 (ORCPT ); Mon, 16 Jul 2007 03:41:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753692AbXGPHlt (ORCPT ); Mon, 16 Jul 2007 03:41:49 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:56503 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753172AbXGPHls (ORCPT ); Mon, 16 Jul 2007 03:41:48 -0400 Date: Mon, 16 Jul 2007 09:41:02 +0200 From: Ingo Molnar To: James Bruce Cc: Thomas Gleixner , Roman Zippel , Mike Galbraith , Linus Torvalds , Andrea Arcangeli , Andi Kleen , Andrew Morton , linux-kernel@vger.kernel.org, Arjan van de Ven , Chris Wright Subject: Re: [PATCH] CFS: Fix missing digit off in wmult table Message-ID: <20070716074102.GA18512@elte.hu> References: <20070711174252.GA16793@elte.hu> <20070711211638.GE18767@one.firstfloor.org> <20070711214649.GK14435@v2.random> <1184302024.6709.11.camel@Homer.simpson.net> <1184355835.12353.321.camel@chaos> <469B0D9E.3030402@andrew.cmu.edu> <20070716070610.GA10907@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070716070610.GA10907@elte.hu> User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7-deb -1.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Ingo Molnar wrote: > * James Bruce wrote: > > > While we're at it, isn't the comment above the wmult table incorrect? > > The multiplier is 1.25, meaning a 25% change per nice level, not 10%. > > yes, the weight multiplier 1.25, but the actual difference in CPU > utilization, when running two CPU intense tasks, is ~10%: > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 8246 mingo 20 0 1576 244 196 R 55 0.0 0:11.96 loop > 8247 mingo 21 1 1576 244 196 R 45 0.0 0:10.52 loop > > so the first task 'wins' +10% CPU utilization (relative to the 50% it > had before), the second task 'loses' -10% CPU utilization (relative to > the 50% it had before). > > so what the comment says is true: > > * The "10% effect" is relative and cumulative: from _any_ nice level, > * if you go up 1 level, it's -10% CPU usage, if you go down 1 level > * it's +10% CPU usage. > > for there to be a ~+10% change in CPU utilization for a task that > races against another CPU-intense task there needs to be a ~25% change > in the weight. in any case more documentation is justified, so i've added some clarification to the comments - see the patch below. Ingo ------------------------> Subject: sched: improve weight-array comments From: Ingo Molnar improve the comments around the wmult array (which controls the weight of niced tasks). Clarify that to achieve a 10% difference in CPU utilization, a weight multiplier of 1.25 has to be used. Signed-off-by: Ingo Molnar --- kernel/sched.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) Index: linux/kernel/sched.c =================================================================== --- linux.orig/kernel/sched.c +++ linux/kernel/sched.c @@ -736,7 +736,9 @@ static void update_curr_load(struct rq * * * The "10% effect" is relative and cumulative: from _any_ nice level, * if you go up 1 level, it's -10% CPU usage, if you go down 1 level - * it's +10% CPU usage. + * it's +10% CPU usage. (to achieve that we use a multiplier of 1.25. + * If a task goes up by ~10% and another task goes down by ~10% then + * the relative distance between them is ~25%.) */ static const int prio_to_weight[40] = { /* -20 */ 88818, 71054, 56843, 45475, 36380, 29104, 23283, 18626, 14901, 11921,