Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759699AbXH1QqL (ORCPT ); Tue, 28 Aug 2007 12:46:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759106AbXH1QpV (ORCPT ); Tue, 28 Aug 2007 12:45:21 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:50954 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758937AbXH1QpT (ORCPT ); Tue, 28 Aug 2007 12:45:19 -0400 Date: Tue, 28 Aug 2007 18:45:07 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Al Boldi , Peter Zijlstra , Mike Galbraith , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: CFS review Message-ID: <20070828164507.GA2969@elte.hu> References: <200708111344.42934.a1426z@gawab.com> <200708280737.53439.a1426z@gawab.com> <200708280823.53663.a1426z@gawab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Content-Length: 1918 Lines: 42 * Linus Torvalds wrote: > On Tue, 28 Aug 2007, Al Boldi wrote: > > > > I like your analysis, but how do you explain that these stalls > > vanish when __update_curr is disabled? > > It's entirely possible that what happens is that the X scheduling is > just a slightly unstable system - which effectively would turn a small > scheduling difference into a *huge* visible difference. i think it's because disabling __update_curr() in essence removes the ability of scheduler to preempt tasks - that hack in essence results in a non-scheduler. Hence the gears + X pair of tasks becomes a synchronous pair of tasks in essence - and thus gears cannot "overload" X. Normally gears + X is an asynchronous pair of tasks, with gears (or xperf, or devel versions of firefox, etc.) not being throttled at all and thus being able to overload/spam the X server with requests. (And we generally want to _reward_ asynchronity and want to allow tasks to overlap each other and we want each task to go as fast and as parallel as it can.) Eventually X's built-in "bad, abusive client" throttling code kicks in, which, AFAIK is pretty crude and might yield to such artifacts. But ... it would be nice for an X person to confirm - and in any case i'll try Al's workload - i thought i had a reproducer but i barked up the wrong tree :-) My laptop doesnt run with the vesa driver, so i have no easy reproducer for now. ( also, it would be nice if Al could try rc4 plus my latest scheduler tree as well - just on the odd chance that something got fixed meanwhile. In particular Mike's sleeper-bonus-limit fix could be related. ) 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/