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    SubjectRe: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks on v3.6
    On 08/06/2012 07:21 PM, John Stultz wrote:
    > On 08/05/2012 09:55 AM, Sasha Levin wrote:
    >> On 07/30/2012 03:17 PM, Avi Kivity wrote:
    >>> Possible causes:
    >>> - the APIC calibration in the guest failed, so it is programming too
    >>> low values into the timer
    >>> - it actually needs 1 us wakeups and then can't keep up (esp. as kvm
    >>> interrupt injection is slowing it down)
    >>>
    >>> You can try to find out by changing
    >>> arch/x86/kvm/lapic.c:start_lapic_timer() to impose a minimum wakeup of
    >>> (say) 20 microseconds which will let the guest live long enough for you
    >>> to ftrace it and see what kind of timers it is programming.
    >> I've kept trying to narrow it down, and found out It's triggerable using adjtimex().
    >>
    >> At that point I've bisected it, and got the following commit (parties Cc'ed):
    >>
    >> commit 5baefd6d84163443215f4a99f6a20f054ef11236
    >> Author: John Stultz <johnstul@us.ibm.com>
    >> Date: Tue Jul 10 18:43:25 2012 -0400
    >>
    >> hrtimer: Update hrtimer base offsets each hrtimer_interrupt
    >>
    >>
    >> I've also confirmed that reverting the commit above on top of linux-next indeed fixes the issue.
    > Hey Sasha,
    > Thanks for the heads up. I don't have a clear sense of what could be wrong here yet, but if you see this with 3.6-rc but not 3.5, could you try the fix(1d17d17484d40f2d5b35c79518597a2b25296996) Ingo just made on tip/timers/urgent?

    I've just tested it, and it didn't solve the issue.


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