Re: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks on v3.6

From: John Stultz
Date: Mon Aug 06 2012 - 14:22:25 EST


On 08/06/2012 10:21 AM, 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().
Sorry, one more question: Could you provide details on how is it trigger-able using adjtimex?

thanks
-john

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