linux-kernel - Re: [PATCH v2] perf tools: Get a perf cgroup more portably in BPF

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Message-ID: <CAM9d7cjpZVeh4D27PWNv4Z=PEH+2TajNte-GkvWJiAuXz5AhBQ@mail.gmail.com>
Date:   Thu, 22 Sep 2022 13:42:08 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Hao Luo <haoluo@...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>,
        Ian Rogers <irogers@...gle.com>,
        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 v2] perf tools: Get a perf cgroup more portably in BPF

Hi Hao,

On Thu, Sep 22, 2022 at 12:36 PM Hao Luo <haoluo@...gle.com> wrote:
>
> On Wed, Sep 21, 2022 at 9:40 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.
> >
>
> I remember using bpf_core_enum_value requires a compiler built-in. So
> the build will fail on old compiler such as clang-11. See [1]. Maybe
> we should surround it with #if
> __has_builtin(__builtin_preserve_enum_value) to be sure.
>
> [1]  https://www.spinics.net/lists/bpf/msg30859.html

Thanks for pointing this out.  As this is a kind of optimization
I think we can fallback to using the existing value if not available.
Will send v3.

Thanks,
Namhyung