Re: [PATCH 2/2] sched/psi: iterate through cgroups directly

["Michal Koutný" <mkoutny@suse.com>]

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On Thu, Feb 16, 2023 at 01:49:22AM +0800, Kairui Song <ryncsn@gmail.com> wrote:
> With rootcg:
> 55718.9 op/s (unpatched) compared to 55862.2 (patched)
> With 5 levels:
> 49975.5 op/s (unpatched) compared to 50778.5 op/s (patched)
> 
> Previous tests are a bit biased since I only run the test for 100 * 3
> times, or maybe it is sensitive to some random kernel structure
> changes.
> 
> But I ignored one important thing in my previous test, that the
> performance actually drops heavily with deeper levers of cgroups:
> With 8 levels:
> 48902.4 op/s (unpatched) compared to 47476.6 op/s (patched)
> With 50 levels of cgroup:
> 25605.7375 op/s (unpatched) compared to 20417.275 op/s (patched)

IIUC, one could also interpret this as the parent caching within
psi_group is effective especially with deep hierarchies.

I'd say practical hierarchies are below 10 levels deep. But yeah, the
averaged results aren't so impressive.

Thanks for sharing your insights,
Michal

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