Re: [RFC bpf-next] Hierarchical Cgroup Stats Collection Using BPF

[Song Liu <song@kernel.org>]

On Wed, Mar 9, 2022 at 12:27 PM Yosry Ahmed <yosryahmed@google.com> wrote:
>
> Hey everyone,
>
> I would like to discuss an idea to facilitate collection of
> hierarchical cgroup stats using BPF programs. We want to provide a
> simple interface for BPF programs to collect hierarchical cgroup stats
> and integrate with the existing rstat aggregation mechanism in the
> kernel. The most prominent use case is the ability to extend memcg
> stats (and histograms) by BPF programs.
>

+ Namhyung,

I forgot to mention this in the office hour. The aggregation efficiency
problem is actually similar to Namhyung's work to use BPF programs
to aggregate perf counters. Check:
     tools/perf/util/bpf_skel/bperf_cgroup.bpf.c

Namhyung's solution is to walk up the cgroup tree on cgroup switch
events. This may not be as efficient as rstat flush logic, but I think it
is good enough for many use cases (unless the cgroup tree is very
deep). It also demonstrates how we can implement some cgroup
logic in BPF.

I hope this helps.

Thanks,
Song

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