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

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Message-ID: <50200AEF.5080904@us.ibm.com>
Date:	Mon, 06 Aug 2012 11:20:31 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Sasha Levin <levinsasha928@...il.com>
CC:	Avi Kivity <avi@...hat.com>, paulmck@...ux.vnet.ibm.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	mingo@...nel.org, a.p.zijlstra@...llo.nl, prarit@...hat.com,
	tglx@...utronix.de
Subject: Re: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks on v3.6

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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