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

Hao Luo
2022-04-27T23:07:43Z

Hi Namhyung,

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

[...]

>
> Signed-off-by: Namhyung Kim <namhyung@kernel.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