linux-kernel - Re: [PATCH 0/2] Quieten softlockup detector on virtualised kernels

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Date:	Mon, 5 Jan 2015 14:09:50 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cyril Bur <cyrilbur@...il.com>
Cc:	linux-kernel@...r.kernel.org, mpe@...erman.id.au,
	drjones@...hat.com, dzickus@...hat.com, mingo@...nel.org,
	uobergfe@...hat.com, chaiw.fnst@...fujitsu.com, cl@...u.com,
	fabf@...net.be, atomlin@...hat.com, benzh@...omium.org
Subject: Re: [PATCH 0/2] Quieten softlockup detector on virtualised kernels

On Mon, 22 Dec 2014 16:06:02 +1100 Cyril Bur <cyrilbur@...il.com> wrote:

> When the hypervisor pauses a virtualised kernel the kernel will observe a jump
> in timebase, this can cause spurious messages from the softlockup detector.
> 
> Whilst these messages are harmless, they are accompanied with a stack trace
> which causes undue concern and more problematically the stack trace in the
> guest has nothing to do with the observed problem and can only be misleading.
> 
> Futhermore, on POWER8 this is completely avoidable with the introduction of
> the Virtual Time Base (VTB) register.

Does this problem apply to other KVM implementations and to Xen?  If
so, what would implementations of running_clock() for those look like? 
If not, why not?


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