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    SubjectRe: [bisected] Clocksource tsc unstable git
    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?

    It's quite easy to reproduce on my setup. I simply run:

    qemu-kvm -net nic,vlan=0,model=virtio -net user -drive file=ubuntu,if=virtio,boot=on -smp 2 -m 512

    and then move the mousepointer in circles in the qemu window. It will stop and
    freeze after a few seconds.
    --
    Markus


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