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

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Message-ID: <20190108104841.GD6808@hirez.programming.kicks-ass.net>
Date:   Tue, 8 Jan 2019 11:48:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrew Murray <andrew.murray@....com>
Cc:     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, boris.ostrovsky@...cle.com,
        jgross@...e.com
Subject: Re: [PATCH v4 10/13] x86: perf/core: use PERF_PMU_CAP_NO_EXCLUDE for
 exclude incapable PMUs

On Mon, Jan 07, 2019 at 04:27:27PM +0000, Andrew Murray wrote:
> For drivers that do not support context exclusion let's advertise the
> PERF_PMU_CAP_NOEXCLUDE capability. This ensures that perf will
> prevent us from handling events where any exclusion flags are set.
> Let's also remove the now unnecessary check for exclusion flags.
> 
> Signed-off-by: Andrew Murray <andrew.murray@....com>
> ---
>  arch/x86/events/amd/ibs.c          | 13 +------------
>  arch/x86/events/amd/power.c        | 10 ++--------
>  arch/x86/events/intel/cstate.c     | 12 +++---------
>  arch/x86/events/intel/rapl.c       |  9 ++-------
>  arch/x86/events/intel/uncore_snb.c |  9 ++-------
>  arch/x86/events/msr.c              | 10 ++--------
>  6 files changed, 12 insertions(+), 51 deletions(-)

You (correctly) don't add CAP_NO_EXCLUDE to the main x86 pmu code, but
then you also don't check if it handles all the various exclude options
correctly/consistently.

Now; I must admit that that is a bit of a maze, but I think we can at
least add exclude_idle and exclude_hv fails in there, nothing uses those
afaict.

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?