linux-kernel - Re: [PATCH v4 10/13] x86: perf/core: use PERF_PMU_CAP_NO

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Date:   Tue, 8 Jan 2019 19:49:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Andrew Murray <andrew.murray@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Russell King <linux@...linux.org.uk>, suzuki.poulose@....com,
        robin.murphy@....com, Michael Ellerman <mpe@...erman.id.au>,
        x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-alpha@...r.kernel.org, jgross@...e.com
Subject: Re: [PATCH v4 10/13] x86: perf/core: use PERF_PMU_CAP_NO_EXCLUDE for
 exclude incapable PMUs

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!