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
