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

[Christian Borntraeger <borntraeger@de.ibm.com>]

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
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