Re: [PATCH 0/2][KVM] guest time accounting

Christian Borntraeger
2007-08-13T14:15:42Z

Am Montag, 13. August 2007 schrieb Laurent Vivier:
> > [copying Ingo and Rusty]

@Avi, seems that sourceforge is mangling the cc list?

> >
> > The patches look good. A couple of comments:
> >
> > - perhaps the new fields should be guarded by a #ifdef CONFIG_HYPERVISOR
> > (selected by CONFIG_KVM)? that way the (minor) additional overhead is
> > only incurred if it can possibly be used. I imagine that our canine
> > cousin will want to use this as well.
>
> There is also a CONFIG_VIRTUALIZATION and a CONFIG_VIRT_CPU_ACCOUNTING (from
> s390 and powerpc) Which one to use ?

CONFIG_VIRT_CPU_ACCOUNTING is used for the precise accouting of user,system,
steal and irq time on these platforms and is not what you want for the on/off
decision.
>
> I'm wondering if we can have a more accurate accounting:
>
> - For the moment we add all system time since the previous entering to the
> VCPU to the guest time (and I guess there is some real system time in
> it ???)
> - Perhaps we can sum nanoseconds spent in the VCPU and add it to cpustat
> when these ns are greater than 1 ms ? (I'm trying to make something in this
way)

If you look at the patch I have posted some minutes ago, I use a method
similar to irq_enter and irq_exit to separate real system time from guest
time.

> > - I think that there is per-task accounting of user time and system
> > time; that should be extended as well.
> it should be easy to do too...

We have to make sure that userspace doesnt break, but yes we should have a
guest time for processes as well.

Christian