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

[Avi Kivity <avi@qumranet.com>]

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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