linux-kernel - Re: [PATCH v2 03/13] perf/x86/amd: add AMD Fam19h Branch Sampling support

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Message-ID: <20211116082923.GX174703@worktop.programming.kicks-ass.net>
Date:   Tue, 16 Nov 2021 09:29:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kim.phillips@....com,
        acme@...hat.com, jolsa@...hat.com, songliubraving@...com,
        mpe@...erman.id.au, maddy@...ux.ibm.com
Subject: Re: [PATCH v2 03/13] perf/x86/amd: add AMD Fam19h Branch Sampling
 support

On Mon, Nov 15, 2021 at 11:48:01PM -0800, Stephane Eranian wrote:
> On Fri, Nov 12, 2021 at 8:02 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Thu, Nov 11, 2021 at 12:44:05AM -0800, Stephane Eranian wrote:
> > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> > > index 38b2c779146f..28559557f966 100644
> > > --- a/arch/x86/events/core.c
> > > +++ b/arch/x86/events/core.c
> > > @@ -683,11 +683,16 @@ void x86_pmu_disable_all(void)
> > >
> > >               if (!test_bit(idx, cpuc->active_mask))
> > >                       continue;
> > > +
> > > +             if (is_amd_brs(hwc))
> > > +                     amd_brs_disable();
> > > +
> > >               rdmsrl(x86_pmu_config_addr(idx), val);
> > >               if (!(val & ARCH_PERFMON_EVENTSEL_ENABLE))
> > >                       continue;
> > >               val &= ~ARCH_PERFMON_EVENTSEL_ENABLE;
> > >               wrmsrl(x86_pmu_config_addr(idx), val);
> > > +
> > >               if (is_counter_pair(hwc))
> > >                       wrmsrl(x86_pmu_config_addr(idx + 1), 0);
> > >       }
> >
> > Please, stick that in amd_pmu_disable_all().
> 
> 
> If I do that, I need to add a for_each_counter() loop to
> amd_pmu_disable_all() but it does not have one call systematically.
> If you are okay with it, then I am fine as well.

Why ? There is only one BRS you can disable it first, and then do the
loop. Same on the enable_all side, enable it once, not per event.
->add/->del can keep a per-event count for sharing purposes, but you
don't need that for {en,dis}able_all, right?