linux-kernel - Re: [PATCH] perf stat: Get a perf cgroup more portably in BPF

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Date:   Wed, 21 Sep 2022 20:53:49 -0700
From:   Ian Rogers <irogers@...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>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, Song Liu <songliubraving@...com>,
        bpf@...r.kernel.org
Subject: Re: [PATCH] perf stat: Get a perf cgroup more portably in BPF

On Wed, Sep 21, 2022 at 8:33 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> The perf_event_cgrp_id can be different on other configurations.
> To be more portable as CO-RE, it needs to get the cgroup subsys id
> using the bpf_core_enum_value() helper.
>
> Suggested-by: Ian Rogers <irogers@...gle.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/util/bpf_skel/bperf_cgroup.bpf.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
> index c72f8ad96f75..35a8e38d3ee3 100644
> --- a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
> +++ b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c
> @@ -57,8 +57,10 @@ static inline int get_cgroup_v1_idx(__u32 *cgrps, int size)
>         __u32 *elem;
>         int level;
>         int cnt;
> +       int perf_id;
>
> -       cgrp = BPF_CORE_READ(p, cgroups, subsys[perf_event_cgrp_id], cgroup);
> +       perf_id = bpf_core_enum_value(enum cgroup_subsys_id, perf_event_cgrp_id);
> +       cgrp = BPF_CORE_READ(p, cgroups, subsys[perf_id], cgroup);

LGTM, do we need the same fix in off cpu?
https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/util/bpf_skel/off_cpu.bpf.c?h=perf/core#n123

Thanks,
Ian

>         level = BPF_CORE_READ(cgrp, level);
>
>         for (cnt = 0; i < MAX_LEVELS; i++) {
> --
> 2.37.3.968.ga6b4b080e4-goog
>