Re: [PATCH 00/13] Implement support for IBS virtualization

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On 9/8/2023 7:01 PM, Peter Zijlstra wrote:
> On Thu, Sep 07, 2023 at 09:19:51PM +0530, Manali Shukla wrote:
> 
>>> I'm not sure I'm fluent in virt speak (in fact, I'm sure I'm not). Is
>>> the above saying that a host can never IBS profile a guest?
>>
>> Host can profile a guest with IBS if VIBS is disabled for the guest. This is
>> the default behavior. Host can not profile guest if VIBS is enabled for guest.
>>
>>>
>>> Does the current IBS thing assert perf_event_attr::exclude_guest is set?
>>
>> Unlike AMD core pmu, IBS doesn't have Host/Guest filtering capability, thus
>> perf_event_open() fails if exclude_guest is set for an IBS event.
> 
> Then you must not allow VIBS if a host cpu-wide IBS counter exists.
> 
> Also, VIBS reads like it can be (ab)used as a filter.

I think I get your point: If host IBS with exclude_guest=0 doesn't capture
guest samples because of VIBS, it is an unintended behavior.

But if a guest cannot use IBS because a host is using it, that is also
unacceptable behavior.

Let me think over it and come back.

- Manali



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