From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753621Ab0KIOXN (ORCPT ); Tue, 9 Nov 2010 09:23:13 -0500 Received: from smtp-out-109.synserver.de ([212.40.180.109]:1438 "EHLO smtp-out-108.synserver.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752224Ab0KIOXL (ORCPT ); Tue, 9 Nov 2010 09:23:11 -0500 X-SynServer-TrustedSrc: 1 X-SynServer-AuthUser: markus@trippelsdorf.de X-SynServer-PPID: 13009 Date: Tue, 9 Nov 2010 14:07:35 +0100 From: Markus Trippelsdorf To: Heiko Carstens Cc: Peter Zijlstra , john stultz , Thomas Gleixner , Borislav Petkov , "linux-kernel@vger.kernel.org" , "hpa@linux.intel.com" , Ingo Molnar , Andreas Herrmann , avi@redhat.com, mtosatti@redhat.com Subject: Re: [bisected] Clocksource tsc unstable git Message-ID: <20101109130735.GA1570@arch.trippelsdorf.de> References: <20101026112052.GA1672@arch.trippelsdorf.de> <20101026131843.GC17852@aftab> <20101026135808.GB1672@arch.trippelsdorf.de> <1288120736.2645.9.camel@localhost> <20101027142622.GA1555@arch.trippelsdorf.de> <20101027182608.GA1580@arch.trippelsdorf.de> <1288208215.3673.16.camel@laptop> <20101109125842.GA8636@osiris.boeblingen.de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101109125842.GA8636@osiris.boeblingen.de.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 09, 2010 at 01:58:42PM +0100, Heiko Carstens wrote: > On Wed, Oct 27, 2010 at 09:36:55PM +0200, Peter Zijlstra wrote: > > On Wed, 2010-10-27 at 20:26 +0200, markus@trippelsdorf.de wrote: > > > > > > 34f971f6f7988be4d014eec3e3526bee6d007ffa is the first bad commit > > > commit 34f971f6f7988be4d014eec3e3526bee6d007ffa > > > Author: Peter Zijlstra > > > Date: Wed Sep 22 13:53:15 2010 +0200 > > > > > > sched: Create special class for stop/migrate work > > > > > > In order to separate the stop/migrate work thread from the SCHED_FIFO > > > implementation, create a special class for it that is of higher priority than > > > SCHED_FIFO itself. > > > > > > This currently solves a problem where cpu-hotplug consumes so much cpu-time > > > that the SCHED_FIFO class gets throttled, but has the bandwidth replenishment > > > timer pending on the now dead cpu. > > > > > > It is also required for when we add the planned deadline scheduling class above > > > SCHED_FIFO, as the stop/migrate thread still needs to transcent those tasks. > > > > > > Tested-by: Heiko Carstens > > > Signed-off-by: Peter Zijlstra > > > LKML-Reference: <1285165776.2275.1022.camel@laptop> > > > Signed-off-by: Ingo Molnar > > > > > > Reverting the commit solves the kvm hang issue. > > > (If this issue is related to my original tsc problem is of course open for > > > debate, but I have a strong hunch it is.) > > > > Too weird,.. what does the hang look like? > > > > Can you generate a sysrq-t dump? The thing I'm looking for is the > > migration/# thread being runnable but not being current. > > > > How can I reproduce this? > > I think there is a bug in pick_next_task_stop() in sched_stopclass.c: > > If a stop-task scheduling class task (well... the migration thread ;) sets > its state to TASK_INTERRUPTIBLE and then gets preempted it will never > scheduled again, because pick_next_task_stop() ignores all tasks with a > state != TASK_RUNNING: > ... > > I would guess something like the below would probably fix it. > Does that make any sense or did I miss something obvious? You missed the fact that Peter already has a patch that fixes the problem, but never bothered to post it in this thread. http://article.gmane.org/gmane.linux.kernel/1058018 -- Markus