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

Christian Borntraeger wrote:

Am Montag, 13. August 2007 schrieb Laurent Vivier:
  

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[copying Ingo and Rusty]
      

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

  

It's not configured to do so.  Can you be more specific?

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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. 
  

Ah, ok.

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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. 

Yes.  This is orthogonal to the current accounting patch and should make 
a nice extension.  It's probably useful with dynamic tick where timer 
interrupts can be rare.


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