linux-kernel - Re: [PATCH 0/4] perf intel-pt: Fix the pipe mode (v1)

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Message-ID: <CAM9d7chU6kTdG0y65_UaD_hW75GezzNJF1ZwjNWq8BUpACAGTA@mail.gmail.com>
Date:   Fri, 27 Jan 2023 15:08:37 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     James Clark <james.clark@....com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org, Leo Yan <leo.yan@...aro.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 0/4] perf intel-pt: Fix the pipe mode (v1)

Hi James,

On Fri, Jan 27, 2023 at 6:42 AM James Clark <james.clark@....com> wrote:
>
>
>
> On 27/01/2023 07:22, Adrian Hunter wrote:
> > On 27/01/23 02:19, Namhyung Kim wrote:
> >> Hello,
> >>
> >> I found some problems in Intel-PT and auxtrace in general with pipe.
> >> In the past it used to work with pipe, but recent code fails.
> >
> > Pipe mode is a problem for Intel PT and possibly other auxtrace users.
>
> Just some info from my side: For Arm Coresight we ended up deprecating
> pipe mode, then not supporting it altogether. First was when we added an
> optional step to peek through all of the data to help with an edge case.
> Then we added a requirement to receive a HW_ID packet before decoding
> which necessitated the peek. You can't peek in pipe mode because you
> need to be able to seek, so it's not supported at all anymore.
>
> For Arm SPE I never tested it with piped data. I suppose I could add a
> test at some point, but I don't really see the usecase.

Yeah, it'd be great if we can have a test for Arm SPE.

Anyway, my work env (Google) requires the pipe mode due to the
restriction in disk usage.  Without the pipe support, it's not possible
to run `perf record` in production.

Thanks,
Namhyung