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

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Date:   Mon, 29 Aug 2022 00:48:02 +0200
From:   KP Singh <kpsingh@...nel.org>
To:     Yosry Ahmed <yosryahmed@...gle.com>
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@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/bpf: simplify cgroup_hierarchical_stats selftest

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)

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


>
>  #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
>