From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932128AbZARIab (ORCPT ); Sun, 18 Jan 2009 03:30:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761339AbZARIaP (ORCPT ); Sun, 18 Jan 2009 03:30:15 -0500 Received: from mx2.redhat.com ([66.187.237.31]:54351 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760940AbZARIaN (ORCPT ); Sun, 18 Jan 2009 03:30:13 -0500 Message-ID: <4972E860.5080206@redhat.com> Date: Sun, 18 Jan 2009 10:29:20 +0200 From: Avi Kivity User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Ingo Molnar CC: Mike Galbraith , Kevin Shanahan , Andrew Morton , a.p.zijlstra@chello.nl, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [git pull] scheduler fixes References: <1231964647.14825.59.camel@laptop> <20090116204049.f4d6ef1c.akpm@linux-foundation.org> <1232173776.7073.21.camel@marge.simson.net> <1232186054.6813.48.camel@marge.simson.net> <1232186877.14073.59.camel@laptop> <1232188484.6813.85.camel@marge.simson.net> <1232193617.14073.67.camel@laptop> <1232194752.6273.5.camel@marge.simson.net> <20090117044316.bda7d0bd.akpm@linux-foundation.org> <1232198574.16303.8.camel@marge.simson.net> <20090117160115.GA31601@elte.hu> In-Reply-To: <20090117160115.GA31601@elte.hu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ingo Molnar wrote: > * Mike Galbraith wrote: > > >> On Sat, 2009-01-17 at 04:43 -0800, Andrew Morton wrote: >> >>> http://bugzilla.kernel.org/show_bug.cgi?id=12465 just popped up - another >>> scheduler regression. It has been bisected. >>> >> Seems pretty clear. I'd suggest reverting it. >> > > We can revert it (and will revert it if no solution is found), but i'd > also like to understand why it happens, because that kind of regression > from this change is unexpected - we might be hiding some bug that could > pop up under less debuggable circumstances, so we need to understand it > while we have a chance. > > Below is the commit in question. Avi, any ideas what makes KVM special > here? Perhaps its use of "preempt notifiers" is causing a problem somehow? > preempt notifiers use should cause additional context switch costs of a few thousand cycles and possible an IPI (if a vcpu was migrated). So I'd suspect scheduling latency here. Is it possible to trace this (the time between a wake up and actual scheduling of a task)? -- error compiling committee.c: too many arguments to function