Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752604AbXIYJlj (ORCPT ); Tue, 25 Sep 2007 05:41:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751842AbXIYJl3 (ORCPT ); Tue, 25 Sep 2007 05:41:29 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:36360 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751132AbXIYJl2 (ORCPT ); Tue, 25 Sep 2007 05:41:28 -0400 Date: Tue, 25 Sep 2007 11:40:40 +0200 From: Ingo Molnar To: Srivatsa Vaddagiri Cc: Mike Galbraith , linux-kernel@vger.kernel.org, Peter Zijlstra , Dhaval Giani , Dmitry Adamushko , Andrew Morton Subject: Re: [git] CFS-devel, latest code Message-ID: <20070925094040.GA28391@elte.hu> References: <20070924214537.GA18980@elte.hu> <1190700652.6482.7.camel@Homer.simpson.net> <1190705759.11910.10.camel@Homer.simpson.net> <1190709207.11226.6.camel@Homer.simpson.net> <20070925091331.GA22905@elte.hu> <20070925094440.GK26289@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070925094440.GK26289@linux.vnet.ibm.com> User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7-deb -1.5 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 Content-Length: 1557 Lines: 43 * Srivatsa Vaddagiri wrote: > On Tue, Sep 25, 2007 at 11:13:31AM +0200, Ingo Molnar wrote: > > ok, i'm too seeing some sort of latency weirdness with > > CONFIG_FAIR_GROUP_SCHED enabled, _if_ there's Xorg involved which runs > > under root uid on my box - and hence gets 50% of all CPU time. > > > > Srivatsa, any ideas? It could either be an accounting buglet (less > > likely, seems like the group scheduling bits stick to the 50% splitup > > nicely), or a preemption buglet. One potential preemption buglet would > > be for the group scheduler to not properly preempt a running task when a > > task from another uid is woken? > > Yep, I noticed that too. > > check_preempt_wakeup() > { > ... > > if (is_same_group(curr, p)) { > ^^^^^^^^^^^^^ > > resched_task(); > } > > } > > Will try a fix to check for preemption at higher levels .. i bet fixing this will increase precision of group scheduling as well. Those long latencies can be thought of as noise as well, and the fair-scheduling "engine" might not be capable to offset all sources of noise. So generally, while we allow a certain amount of lag in preemption decisions (wakeup-granularity, etc.), with which the fairness engine will cope just fine, we do not want to allow unlimited lag. Ingo - 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/