linux-kernel - Re: [PATCH v3] perf evsel: Fix missing exclude

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Date:   Sat, 6 Nov 2021 16:24:01 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ravi Bangoria <ravi.bangoria@....com>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Kim Phillips <kim.phillips@....com>
Subject: Re: [PATCH v3] perf evsel: Fix missing exclude_{host,guest} setting

Em Fri, Nov 05, 2021 at 11:00:29AM -0700, Namhyung Kim escreveu:
> Hello,
> 
> On Wed, Nov 3, 2021 at 12:22 AM Ravi Bangoria <ravi.bangoria@....com> wrote:
> >
> > > The current logic for the perf missing feature has a bug that it can
> > > wrongly clear some modifiers like G or H.  Actually some PMUs don't
> > > support any filtering or exclusion while others do.  But we check it
> > > as a global feature.
> >
> > (Sorry to pitch in bit late)
> >
> > AMD has one more problem on a similar line. On AMD, non-precise and
> > precise sampling are provided by core and IBS pmu respectively. Plus,
> > core pmu has filtering capability but IBS does not. Perf by default
> > sets precise_ip=3 and exclude_guest=1 and goes on decreasing precise_ip
> > with exclude_guest set until perf_event_open() succeeds. This is
> > causing perf to always fallback to core pmu (non-precise mode) even if
> > it's perfectly feasible to do precise sampling. Do you guys think this
> > problem should also be addressed while designing solution for Namhyung's
> > patch or solve it seperately like below patch:
> >
> > ---><---
> >
> > From 48808299679199c39ff737a30a7f387669314fd7 Mon Sep 17 00:00:00 2001
> > From: Ravi Bangoria <ravi.bangoria@....com>
> > Date: Tue, 2 Nov 2021 11:01:12 +0530
> > Subject: [PATCH] perf/amd/ibs: Don't set exclude_guest by default
> >
> > Perf tool sets exclude_guest by default while calling perf_event_open().
> > Because IBS does not have filtering capability, it always gets rejected
> > by IBS PMU driver and thus perf falls back to non-precise sampling. Fix
> > it by not setting exclude_guest by default on AMD.
> >
> > Before:
> >   $ sudo ./perf record -C 0 -vvv true |& grep precise
> >     precise_ip                       3
> >   decreasing precise_ip by one (2)
> >     precise_ip                       2
> >   decreasing precise_ip by one (1)
> >     precise_ip                       1
> >   decreasing precise_ip by one (0)
> >
> > After:
> >   $ sudo ./perf record -C 0 -vvv true |& grep precise
> >     precise_ip                       3
> >   decreasing precise_ip by one (2)
> >     precise_ip                       2
> >
> > Reported-by: Kim Phillips <kim.phillips@....com>
> > Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
> 
> It'd be nice if it can cover explicit -e cycles:pp as well.  Anyway,

Ravi, please consider Namhyung's request, a patch on top as I'm adding
this already.
 
> Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks, applied.

- Arnaldo