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

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Date:   Wed, 8 Feb 2023 22:57:14 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Kairui Song <kasong@...cent.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Chengming Zhou <zhouchengming@...edance.com>,
        Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kairui Song <ryncsn@...il.com>
Subject: Re: [PATCH 2/2] sched/psi: iterate through cgroups directly

On Wed, Feb 08, 2023 at 02:20:12PM -0500, Johannes Weiner <hannes@...xchg.org> wrote:
> Hm, I don't think it does. It sets up *iter to point to the parent for
> the _next() call, but it returns task_dfl_cgroup()->psi. The next call
> does the same: cgroup = *iter, *iter = parent, return cgroup->psi.

You are right.

> It could be a bit more readable to have *iter always point to the
> current cgroup - but no strong preference either way from me:

A casually reading half-brain finds this more idiomatic :)

I just hope the "preloading" of the parent via iter isn't crucial to the
performance change.

Kairui, I like this reorganization and its effect!

Michal