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

[Cyril Bur <cyrilbur@gmail.com>]

On Mon, 2015-01-05 at 14:09 -0800, Andrew Morton wrote:
> On Mon, 22 Dec 2014 16:06:02 +1100 Cyril Bur <cyrilbur@gmail.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?
Yes the problem should appear on other KVM implementations, not really
sure about Xen but I don't see why the problem wouldn't crop up.

x86 do have a method for dealing with it in the softlockup detector,
they've added a check in the softlockup using a paravirtualised clock
where the guest can discover if it had been paused, Xen could be using
too.
It doesn't appear s390 do anything.

Thanks,

Cyril
> 
>