linux-kernel - Re: [PATCH v7 00/13] perf/x86/amd: Add AMD Fam19h Branch Sampling support

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Message-ID: <CABPqkBQ6ZyqSzQyJeNW5GE22V1sygB3zz5JQ45AT1TxMnwWScg@mail.gmail.com>
Date:   Tue, 29 Mar 2022 16:47:52 -0700
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,
        rafael@...nel.org, ravi.bangoria@....com, Sandipan.Das@....com
Subject: Re: [PATCH v7 00/13] perf/x86/amd: Add AMD Fam19h Branch Sampling support

On Tue, Mar 29, 2022 at 2:58 PM Stephane Eranian <eranian@...gle.com> wrote:
>
> On Fri, Mar 25, 2022 at 1:29 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Thu, Mar 24, 2022 at 10:31:38PM -0700, Stephane Eranian wrote:
> > > On Thu, Mar 24, 2022 at 7:59 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > > >
> > > > On Tue, Mar 22, 2022 at 03:15:04PM -0700, Stephane Eranian wrote:
> > > > > V7 makes the following changes:
> > > > >    - rebased to 5.17-rc8
> > > > >    - Restrict BRS to be used only with RETIRED_TAKEN_BRANCH event in order to
> > > > >      avoid adding more skid to other events in case that are monitored
> > > > >      concurrently
> > > > >    - fixed bugs in the perf tool enhanced error handling for IBS and BRS
> > > >
> > > > But afaict you failed to pick up the build fixes I did in my tree :/ Let
> > > > me try and be careful preserving those while munging this in.
> > >
> > > Sorry. I missed that. I can resubmit if you prefer.
> >
> > Nah, fixed it up again.. Even converted to static_call() this time.
> >
> > Could you please test this branch?
>
> Started testing. BRS does not come up so far. Let me debug this.
>
False alarm. I had not forced the config option. With the config
option enabled, it works as expected.
I just found a minor issue in case BRS is not enabled. To be
consistent, we should do:

--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1265,7 +1265,7 @@ static inline s64 amd_brs_adjust_period(s64 period)
 #else
 static inline int amd_brs_init(void)
 {
-       return 0;
+       return -EOPNOTSUPP;
 }

Thanks.

> >
> >   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=perf/amd
> >
> > I've since done more Changelog edits, and I should do a comment with the
> > static_call_mod() usage, but I think this ought to work.
> >
> > At least it now actually builds...