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

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Message-ID: <CAM9d7ch9iSKYwqT_oV-X2-Yr9rSjKB2R_qFS+t7ro8xMm-VPKg@mail.gmail.com>
Date:   Wed, 21 Sep 2022 21:18:29 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
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 <linux-perf-users@...r.kernel.org>,
        Song Liu <songliubraving@...com>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH] perf stat: Get a perf cgroup more portably in BPF

Hi Ian,

On Wed, Sep 21, 2022 at 8:54 PM Ian Rogers <irogers@...gle.com> wrote:
>
> 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

Right, will send v2.

Thanks,
Namhyung