Messages in this thread | | | Date | Tue, 9 Nov 2010 14:07:35 +0100 | From | Markus Trippelsdorf <> | Subject | Re: [bisected] Clocksource tsc unstable git |
| |
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 <a.p.zijlstra@chello.nl> > > > 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 <heiko.carstens@de.ibm.com> > > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > > > LKML-Reference: <1285165776.2275.1022.camel@laptop> > > > Signed-off-by: Ingo Molnar <mingo@elte.hu> > > > > > > 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
| |