linux-kernel - Re: [PATCH] selftests/bpf: simplify cgroup_hierarchical

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Message-ID: <CAJD7tkZtUk8jmtEk559_njcPstyJ5td1xSKPGsqrbggnB6wADg@mail.gmail.com>
Date:   Mon, 29 Aug 2022 10:24:15 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     KP Singh <kpsingh@...nel.org>
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Mykola Lysenko <mykolal@...com>, Song Liu <song@...nel.org>,
        Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf <bpf@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests/bpf: simplify cgroup_hierarchical_stats selftest

On Sun, Aug 28, 2022 at 3:48 PM KP Singh <kpsingh@...nel.org> wrote:
>
> On Sat, Aug 27, 2022 at 1:06 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> >
> > The cgroup_hierarchical_stats selftest is complicated. It has to be,
> > because it tests an entire workflow of recording, aggregating, and
> > dumping cgroup stats. However, some of the complexity is unnecessary.
> > The test now enables the memory controller in a cgroup hierarchy, invokes
> > reclaim, measure reclaim time, THEN uses that reclaim time to test the
> > stats collection and aggregation. We don't need to use such a
> > complicated stat, as the context in which the stat is collected is
> > orthogonal.
> >
> > Simplify the test by using a simple stat instead of reclaim time, the
> > total number of times a process has ever entered a cgroup. This makes
> > the test simpler and removes the dependency on the memory controller and
> > the memory reclaim interface.
> >
> > Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
>
> Acked-by: KP Singh <kpsingh@...nel.org>
>
> > ---
> >
> > When the test failed on Alexei's setup because the memory controller was
> > not enabled I realized this is an unnecessary dependency for the test,
> > which inspired this patch :) I am not sure if this prompt a Fixes tag as
> > the test wasn't broken.
>
> yeah, this is an improvement, I don't think a fixes tag is needed here.
>
> >
> > ---
> >  .../prog_tests/cgroup_hierarchical_stats.c    | 157 ++++++---------
> >  .../bpf/progs/cgroup_hierarchical_stats.c     | 181 ++++++------------
> >  2 files changed, 118 insertions(+), 220 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c b/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
> > index bed1661596f7..12a6d4ddbd77 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c
> > @@ -1,6 +1,9 @@
> >  // SPDX-License-Identifier: GPL-2.0-only
> >  /*
> > - * Functions to manage eBPF programs attached to cgroup subsystems
> > + * This test runs a BPF program that keeps a stat of the number of processes
> > + * that ever attached to a cgroup, and makes sure that BPF integrates well with
> > + * the rstat framework to efficiently collect those stat percpu to avoid
> > + * locking, and to efficiently aggregate the stat across the hierarchy.
> >   *
> >   * Copyright 2022 Google LLC.
> >   */
> > @@ -21,8 +24,10 @@
> >  #define PAGE_SIZE 4096
> >  #define MB(x) (x << 20)
> >
> > +#define PROCESSES_PER_CGROUP 3
> > +
> >  #define BPFFS_ROOT "/sys/fs/bpf/"
> > -#define BPFFS_VMSCAN BPFFS_ROOT"vmscan/"
> > +#define BPFFS_ATTACH_COUNTERS BPFFS_ROOT"attach_counters/"
>
> minor nit: Is there a missing space here?
> i.e
>
> #define BPFFS_ATTACH_COUNTERS BPFFS_ROOT "attach_counters/"
>
> (this was a case in the line you changed so I am not sure if it's intentional)
>

Thanks for taking a look! Yeah I forgot that even if I added a space
there C will still concatenate those strings without adding any
spaces, so I guess it is better with that space.

> The rest looks good to me, so  maintainers could, potentially, push it
> with the minor edit if needed?

Yeah if that space can be added that would be great. Otherwise I can send a v2.

>
>
> >
> >  #define CG_ROOT_NAME "root"
> >  #define CG_ROOT_ID 1
> > @@ -79,7 +84,7 @@ static int setup_bpffs(void)
> >                 return err;
> >
> >
>
> [...]
>
> > -       return 1;
> > +       return 0;
> >  }
> > --
> > 2.37.2.672.g94769d06f0-goog
> >