linux-kernel - Re: soft lockup detector & virtualisation

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Date:	Thu, 16 Feb 2012 20:57:40 -0500
From:	Eric B Munson <emunson@...bm.net>
To:	john stultz <johnstul@...ibm.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: soft lockup detector & virtualisation

On Thu, 16 Feb 2012 17:39:38 -0800, john stultz wrote:
> On Thu, Feb 16, 2012 at 3:15 PM, Dave Jones <davej@...hat.com> wrote:
>> Lately I've noticed quite a few soft lockup bugs being reported.
>> In many of them, they're coming from inside virtual guests.
>>
>> Is the softlockup detector fundamentally broken in this situation ?
>>
>> If the host doesn't schedule the guest for whatever reason,
>> or the user suspends the VM and resumes it later ?
>>
>> Here's the most recent example:
>> https://bugzilla.redhat.com/attachment.cgi?id=563767
>>
>> In many of these, the code where it's "stuck" isn't anything
>> special, which is why I think the guest just hasn't had a
>> timeslice in 185 seconds.
>>
>> Is there some way we can perhaps detect we're running virtualised,
>> and disable the detector automatically ?
>
> I think Eric's work (See "Add check for suspended vm in softlockup
> detector" sent out today) tries to address this issue.
>
> thanks
> -john


The work I have been doing specifically handles the case where the 
hypervisor suspends the guest.  There is talk of extending that work to 
handle preemption as well, which I think will cover your use case.

Eric
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