linux-kernel - Re: [RFC] libperf: Add support for user space counter access

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Date:   Mon, 10 Aug 2020 12:11:23 -0600
From:   Rob Herring <robh@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC] libperf: Add support for user space counter access

On Sat, Aug 8, 2020 at 4:22 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Fri, Aug 07, 2020 at 05:05:17PM -0600, Rob Herring wrote:
> > x86 and arm64 can both support direct access of event counters in
> > userspace. The access sequence is less than trivial and currently exists
> > in perf test code (tools/perf/arch/x86/tests/rdpmc.c) with copies in
> > projects such as PAPI and libpfm4.
> >
> > Patches to add arm64 userspace support are pending[1].
> >
> > For this RFC, looking for a yes, seems like a good idea, or no, go away we
> > don't want this in libperf.
>
> hi,
> looks great!
>
> I wanted to add this for very long time.. so yes, we want this ;-)

Thanks for the quick feedback. Would this be better implemented as a
fast path for perf_evsel__read()? If so, how to get the mmap data
which is associated with a evlist rather than a evsel?

Rob