Re: [bisected] Clocksource tsc unstable git

Peter Zijlstra
2010-10-27T19:37:23Z

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?