Re: [PATCH v2 0/4] implement vcpu preempted check

[Peter Zijlstra]

On Wed, Jul 06, 2016 at 12:44:58PM +0200, Paolo Bonzini wrote:
> > Paolo, could you help out with an (x86) KVM interface for this?
> 
> If it's just for spin loops, you can check if the version field in the
> steal time structure has changed.

That would require remembering the old value, no?

That would work with a previous interface proposal, see:

  http://lkml.kernel.org/r/1466937715-6683-2-git-send-email-xinhui.pan@xxxxxxxxxxxxxxxxxx

the vcpu_get_yield_count() thing would match that I think.

However the current proposal:

  http://lkml.kernel.org/r/1467124991-13164-2-git-send-email-xinhui.pan@xxxxxxxxxxxxxxxxxx

dropped that in favour of only vcpu_is_preempted(), which requires being
able to tell if a (remote) vcpu is currently running or not, which iirc,
isn't possible with the steal time sequence count.