Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os statistics from host side

Avi Kivity
2010-04-14T09:57:50Z

On 04/14/2010 12:43 PM, Sheng Yang wrote:
> On Wednesday 14 April 2010 17:20:15 Avi Kivity wrote:
>
>> On 04/14/2030 12:05 PM, Zhang, Yanmin wrote:
>>
>>> Here is the new patch of V3 against tip/master of April 13th
>>> if anyone wants to try it.
>>>
>> Thanks for persisting despite the flames.
>>
>> Can you please separate arch/x86/kvm part of the patch? That will make
>> for easier reviewing, and will need to go through separate trees.
>>
>> Sheng, did you make any progress with the NMI injection issue?
>>
> Yes, though some other works interrupt me lately...
>
> The very first version has issue due to SELF_IPI mode can't be used to send
> NMI according to SDM. That's the reason why x2apic don't have way to do this.
>

Yes, I see that now. Looks like others have the same questions...

> But later I found another issue of fail to inspect inside the guest. I think
> it's due to NMI is asynchronous event, though it should be triggered very
> quickly, you can't guarantee that the handler would be triggered before the
> state(current_vcpu) is cleared with current code.
>
> Maybe just extended the "guest state" region would be fine, if the latency is
> stable enough(though I think it maybe platform depended). I am working on this
> now.
>

I wouldn't like to depend on model specific behaviour.

One option is to read all the information synchronously and store it in
a per-cpu area with atomic instructions, then queue the NMI. Another
option is to have another callback which tells us that the NMI is done,
and have a busy loop wait until the NMI is delivered.

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