Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755102AbZD2KZH (ORCPT ); Wed, 29 Apr 2009 06:25:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751952AbZD2KYx (ORCPT ); Wed, 29 Apr 2009 06:24:53 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:48788 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751490AbZD2KYx (ORCPT ); Wed, 29 Apr 2009 06:24:53 -0400 Date: Wed, 29 Apr 2009 12:24:09 +0200 From: Ingo Molnar To: Martin Schwidefsky Cc: Eric Dumazet , Andrew Morton , Andrew Gallatin , linux-kernel@vger.kernel.org, rick.jones2@hp.com, brice@myri.com, Paul Mackerras , Benjamin Herrenschmidt Subject: Re: [PATCH] sched: account system time properly Message-ID: <20090429102409.GB2373@elte.hu> References: <49F078FA.6010507@myri.com> <20090428163004.46733752.akpm@linux-foundation.org> <49F7DF44.8090907@cosmosbay.com> <49F805C9.9070303@cosmosbay.com> <20090429100840.77359cae@skybase> <49F81BC3.2050805@cosmosbay.com> <20090429114801.09637e46@skybase> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20090429114801.09637e46@skybase> User-Agent: Mutt/1.5.18 (2008-05-17) 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=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3220 Lines: 77 * Martin Schwidefsky wrote: > On Wed, 29 Apr 2009 11:20:03 +0200 > Eric Dumazet wrote: > > > Martin Schwidefsky a ?crit : > > > On Wed, 29 Apr 2009 09:46:17 +0200 > > > Eric Dumazet wrote: > > > > > >> Eric Dumazet a ?crit : > > >>> Andrew Morton a ?crit : > > >>> > > >>> So, if IRQs are interrupting idle task, I guess if (p != rq->idle) will be false. > > >>> > > > > > > If an IRQ interrupts the idle task the tick is supposed to be accounted > > > as an idle tick. Only if the IRQ interrupted the system while it has > > > been in hardirq or softirq processing then it should be accounted as > > > system tick. > > > > > >> Maybe following patch is needed ? > > >> > > >> [PATCH] sched: account system time properly > > >> > > >> When idle task is interrupted by an IRQ, time accounting considers CPU is idle, > > >> even while it should account for hard or softirq. > > >> > > >> Signed-off-by: Eric Dumazet > > >> > > >> diff --git a/kernel/sched.c b/kernel/sched.c > > >> index b902e58..26efa47 100644 > > >> --- a/kernel/sched.c > > >> +++ b/kernel/sched.c > > >> @@ -4732,7 +4732,7 @@ void account_process_tick(struct task_struct *p, int user_tick) > > >> > > >> if (user_tick) > > >> account_user_time(p, one_jiffy, one_jiffy_scaled); > > >> - else if (p != rq->idle) > > >> + else if ((p != rq->idle) || (irq_count() != HARDIRQ_OFFSET)) > > >> account_system_time(p, HARDIRQ_OFFSET, one_jiffy, > > >> one_jiffy_scaled); > > >> else > > > > > > That patch makes a lot of sense to me. Does it fix the problem? > > > > > > > Yes it does, on my machine at least : > > > > 11:18:48 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %idle > > 11:18:58 AM all 0.00 0.00 0.00 0.00 0.21 0.69 0.00 0.00 99.10 > > 11:18:58 AM 0 0.00 0.00 0.00 0.00 1.70 5.50 0.00 0.00 92.80 << HERE >> > > 11:18:58 AM 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 > > 11:18:58 AM 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 > > 11:18:58 AM 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 > > 11:18:58 AM 4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 > > 11:18:58 AM 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 > > 11:18:58 AM 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 > > 11:18:58 AM 7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 > > Very good. Acked-by: Martin Schwidefsky Thanks. Eric, mind (re-)sending the patch with Martin's ack included, and with either a suitable impact-line footer or an extra paragraph that describes the bug you found (and how it shows up in practice) and how the patch fixed that problem. Thanks, 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/