linux-kernel - Re: [PATCH 2/4] perf record: Enable off-cpu analysis with BPF

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Message-ID: <CA+khW7gvDaDiA458StkOEvUfvr1Rx4d65+530z2tq52VkJqaoA@mail.gmail.com>
Date:   Wed, 27 Apr 2022 16:07:25 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     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>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Song Liu <songliubraving@...com>, bpf@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Blake Jones <blakejones@...gle.com>
Subject: Re: [PATCH 2/4] perf record: Enable off-cpu analysis with BPF

Hi Namhyung,

On Fri, Apr 22, 2022 at 8:05 AM Namhyung Kim <namhyung@...nel.org> wrote:
>

[...]

>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/Makefile.perf               |   1 +
>  tools/perf/builtin-record.c            |  21 +++
>  tools/perf/util/Build                  |   1 +
>  tools/perf/util/bpf_off_cpu.c          | 208 +++++++++++++++++++++++++
>  tools/perf/util/bpf_skel/off_cpu.bpf.c | 137 ++++++++++++++++
>  tools/perf/util/off_cpu.h              |  22 +++
>  6 files changed, 390 insertions(+)
>  create mode 100644 tools/perf/util/bpf_off_cpu.c
>  create mode 100644 tools/perf/util/bpf_skel/off_cpu.bpf.c
>  create mode 100644 tools/perf/util/off_cpu.h
>

[...]

> diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> new file mode 100644
> index 000000000000..2bc6f7cc59ea
> --- /dev/null
> +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
>
> +struct {
> +       __uint(type, BPF_MAP_TYPE_HASH);
> +       __uint(key_size, sizeof(__u32));
> +       __uint(value_size, sizeof(struct tstamp_data));
> +       __uint(max_entries, MAX_ENTRIES);
> +} tstamp SEC(".maps");

I think using task local storage for this tstamp would be more
efficient. There is an example in
tools/bpf/runqslower/runqslower.bpf.c