linux-kernel - Re: [PATCH bpf-next v6 8/8] selftests/bpf: add a selftest for cgroup hierarchical stats collection

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Date:   Mon, 1 Aug 2022 15:59:54 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        cgroups@...r.kernel.org, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        KP Singh <kpsingh@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Michal Koutny <mkoutny@...e.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        David Rientjes <rientjes@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Yosry Ahmed <yosryahmed@...gle.com>
Subject: Re: [PATCH bpf-next v6 8/8] selftests/bpf: add a selftest for cgroup
 hierarchical stats collection

On Mon, Aug 1, 2022 at 3:00 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Mon, Aug 1, 2022 at 10:54 AM Hao Luo <haoluo@...gle.com> wrote:
> >
[...]
> > ---
> >  .../prog_tests/cgroup_hierarchical_stats.c    | 358 ++++++++++++++++++
> >  .../bpf/progs/cgroup_hierarchical_stats.c     | 218 +++++++++++
> >  2 files changed, 576 insertions(+)
> >  create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c
> >
>
> [...]
>
> > +extern void cgroup_rstat_updated(struct cgroup *cgrp, int cpu) __ksym;
> > +extern void cgroup_rstat_flush(struct cgroup *cgrp) __ksym;
> > +
> > +static struct cgroup *task_memcg(struct task_struct *task)
> > +{
> > +       return task->cgroups->subsys[memory_cgrp_id]->cgroup;
>
> memory_cgrp_id is kernel-defined internal enum which actually can
> change based on kernel configuration (i.e., which cgroup subsystems
> are enabled or not), is that right?
>
> In practice you wouldn't hard-code it, it's better to use
> bpf_core_enum_value() to capture enum's value in CO-RE-relocatable
> way.
>
> So it might be a good idea to demonstrate that here.
>

Makes sense. Will use bpf_core_enum_value. Thanks!

> > +}
> > +
> > +static uint64_t cgroup_id(struct cgroup *cgrp)
> > +{
> > +       return cgrp->kn->id;
> > +}
> > +
>
> [...]