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

Avi Kivity
2007-08-13T14:19:49Z

Christian Borntraeger wrote:
> Am Montag, 13. August 2007 schrieb Laurent Vivier:
>
>>> [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?

>>> 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.

>> 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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