Re: [PATCH v4 10/13] x86: perf/core: use PERF_PMU_CAP_NO_EXCLUDE for exclude incapable PMUs

[Peter Zijlstra]

On Tue, Jan 08, 2019 at 11:36:33AM -0500, Boris Ostrovsky wrote:
> On 1/8/19 5:48 AM, Peter Zijlstra wrote:

> > On the various exclude options; they are as follows (IIUC):
> >
> >   - exclude_guest: we're a HV/host-kernel and we don't want the counter
> >                    to run when we run a guest context.
> >
> >   - exclude_host: we're a HV/host-kernel and we don't want the counter
> >                   to run when we run in host context.
> >
> >   - exclude_hv: we're a guest and don't want the counter to run in HV
> >                 context.
> >
> > Now, KVM always implies exclude_hv afaict (for guests), I'm not sure
> > what, if anything Xen does on x86 (IIRC Brendan Gregg once said perf
> > works on Xen) -- nor quite sure who to ask, Boris, Jeurgen?
> 
> perf does work inside guests.
> 
> VPMU is managed by the Xen and it presents to the guest only samples
> that are associated with the guest. So from that perspective exclude_hv
> doesn't seem to be needed.
> 
> There is a VPMU mode that allows profiling whole system (host and
> guests) from dom0, and this where exclude_hv might be useful. But this
> mode, ahem, needs some work.

Thanks Boris!