linux-kernel - Re: Invalid event (cycles:pp) in per-thread mode, enable system wide with '-a'.

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Message-ID: <CAKwvOdk6TTNhu_+FdONTXPo9Z8u5D4-5kf-rMN8oK4+6fMyc-w@mail.gmail.com>
Date:   Wed, 5 Oct 2022 14:55:54 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     Slade Watkins <srw@...dewatkins.net>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        Namhyung Kim <namhyung@...il.com>,
        Stephane Eranian <eranian@...gle.com>,
        Kees Cook <keescook@...omium.org>, sandipan.das@....com,
        Bill Wendling <morbo@...gle.com>,
        clang-built-linux <llvm@...ts.linux.dev>,
        Yonghong Song <yhs@...com>
Subject: Re: Invalid event (cycles:pp) in per-thread mode, enable system wide
 with '-a'.

+ Stephane, Kees, Sandipan, Bill, ClangBuiltLinux mailing list, Yonghong
https://www.spinics.net/lists/linux-perf-users/msg23103.html
starts the thread, for context.

On Thu, Sep 29, 2022 at 9:32 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
>
> On 30-Sep-22 9:56 AM, Namhyung Kim wrote:
> > Hello,
> >
> > On Thu, Sep 29, 2022 at 8:49 PM Ian Rogers <irogers@...gle.com> wrote:
> >>
> >> On Thu, Sep 29, 2022 at 3:10 PM Slade Watkins <srw@...dewatkins.net> wrote:
> >>>
> >>> Hey Nick,
> >>>
> >>>> On Sep 29, 2022, at 5:54 PM, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> >>>>
> >>>> I remember hearing rumblings about issues with zen 2, LBR, vs zen 3.
> >>>> Is this a known issue, or am I holding it wrong?
> >>>
> >>> Hm… I also remember this. I have a Zen 2 based system that I can do testing on, so I will do so when I’m able.
> >>>
> >>> If I discover something of note, I’ll get back to you.
> >>>
> >>> Cheers,
> >>> -srw
> >>>
> >>
> >> LBR isn't yet supported for Zen but is coming:
> >> https://lore.kernel.org/lkml/166155216401.401.5809694678609694438.tip-bot2@tip-bot2/
> >> I'd recommend frame-pointers.

Having to recompile is less than ideal for my workflow.  I have added a note to
https://github.com/ClangBuiltLinux/profiling/tree/main/perf#errors
Please let me know how I might improve the documentation.

> >>
> >> +Ravi who may be able to say if there are any issues with the precise
> >> sampling on AMD.
> >
> > Afaik cvcles:pp will use IBS but it doesn't support per-task profiling
> > since it has no task context.  Ravi is working on it..
>
> Right.
> https://lore.kernel.org/lkml/20220829113347.295-1-ravi.bangoria@amd.com

Cool, thanks for working on this Ravi.

I'm not sure yet whether I may replace the kernel on my corporate
provided workstation, so I'm not sure yet I can help test that patch.

Can you confirm that
$ perf record -e cycles:pp --freq=128 --call-graph lbr -- <command to profile>

works with just that patch applied? Or is there more work required?
What is the status of that patch?

For context, we had difficulty upstreaming support for instrumentation
based profile guided optimizations in the Linux kernel.
https://lore.kernel.org/lkml/CAHk-=whqCT0BeqBQhW8D-YoLLgp_eFY=8Y=9ieREM5xx0ef08w@mail.gmail.com/
We'd like to be able to use either instrumentation or sampling to
optimize our builds.  The major barrier to sample based approaches are
architecture / micro architecture issues with sample based profile
data collection, and bitrot of data processing utilities.
https://github.com/google/autofdo/issues/144
-- 
Thanks,
~Nick Desaulniers