Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761423AbXEJRFo (ORCPT ); Thu, 10 May 2007 13:05:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760551AbXEJRF3 (ORCPT ); Thu, 10 May 2007 13:05:29 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.142]:46510 "EHLO e2.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760241AbXEJRF2 (ORCPT ); Thu, 10 May 2007 13:05:28 -0400 Date: Thu, 10 May 2007 22:43:12 +0530 From: Srivatsa Vaddagiri To: William Lee Irwin III Cc: Ingo Molnar , Mike Galbraith , linux-kernel@vger.kernel.org, Linus Torvalds , Andrew Morton , Con Kolivas , Nick Piggin , Arjan van de Ven , Peter Williams , Thomas Gleixner , caglar@pardus.org.tr, Willy Tarreau , Gene Heskett , Mark Lord , tingy@cs.umass.edu, tong.n.li@intel.com Subject: Re: Definition of fairness (was Re: [patch] CFS scheduler, -v11) Message-ID: <20070510171312.GB27462@in.ibm.com> Reply-To: vatsa@in.ibm.com References: <20070508150431.GA26977@elte.hu> <20070509180205.GA27462@in.ibm.com> <20070509202418.GE31925@holomorphy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070509202418.GE31925@holomorphy.com> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2156 Lines: 43 On Wed, May 09, 2007 at 01:24:18PM -0700, William Lee Irwin III wrote: > It's not even feasible much of the time. Suppose your task ran for > 100ms then slept for 900ms. It can't get more than 10% of the CPU in > any scheduler, work-conserving or not. sure. The question of fairnes arises when such a task has to "fight" for space/cputime in those 100ms, resulting in lesser than 10% bandwidth. Having some statistics shown on cpu demand vs obtained bandwidth may be good? > Fairness applies only to running tasks. The fair share of CPU must be > granted while the task is running. As for sleep, it has to use its > fair share of CPU or lose it. The numerous of pathologies that arise > from trying to credit tasks for sleep in this fashion this are why > fairness in the orthodox sense I describe is now such a high priority. > > However, it is possible to credit tasks for sleep in other ways. For > instance, EEVDF (which is very close to CFS) has a deadline parameter > expressing latency in addition to one expressing bandwidth that could, > in principle, be used for the purpose of crediting sleeping tasks. It's > not clear to me whether trying to use it for such purposes would be > sound, or, for that matter, whether tasks should receive latency > credits for sleep as opposed to other sorts of behaviors even if > utilizing the latency parameter for credits and bonuses for various > sorts of behavior is sound. I guess fairness interval also matters, as Mike pointed out. Over shorter intervals, it may appear more fair to such sleeping tasks than over longer intervals. Btw CFS seems to leave this fairness interval undefined (its dependent on N, number of tasks and sysctl_sched_granularity?). I suspect container/database/webserver workloads would like to receive such latency/bandwidth credits for sleep. Will check with our database/workload management folks on this. -- Regards, vatsa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/