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

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Message-ID: <CABPqkBQ4BCswvNPpkO79dBamhudikz1cGCXFpwAp9xsTb3F8xQ@mail.gmail.com>
Date:   Tue, 16 Nov 2021 23:23:39 -0800
From:   Stephane Eranian <eranian@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 Tue, Nov 16, 2021 at 12:29 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> 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?

Ok, I made the changes you suggested. It looks closer to the way LBR is handled.
However, this means that there is no path by which you can get to
amd_pmu_disable_event()
without having gone through amd_pmu_disable_all(). Is that always the
case? And same thing
on the enable side.