From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny-IBi9RG/b67k@public.gmane.org>
Subject: Re: [PATCH 2/2] sched/psi: iterate through cgroups directly
Date: Wed, 8 Feb 2023 22:57:14 +0100
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To: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
Cc: Kairui Song <kasong-1Nz4purKYjRBDgjK7y7TUQ@public.gmane.org>, Suren Baghdasaryan <surenb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Chengming Zhou <zhouchengming-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Kairui Song <ryncsn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

On Wed, Feb 08, 2023 at 02:20:12PM -0500, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.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