Date:   Wed, 8 Feb 2023 22:57:14 +0100
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Kairui Song <kasong@tencent.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Chengming Zhou <zhouchengming@bytedance.com>,
        Tejun Heo <tj@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, Kairui Song <ryncsn@gmail.com>
Subject: Re: [PATCH 2/2] sched/psi: iterate through cgroups directly
Message-ID: <Y+QaunjOmvJf3NTU@blackbook>
References: <20230208161654.99556-1-ryncsn@gmail.com>
 <20230208161654.99556-3-ryncsn@gmail.com>
 <20230208172956.GF24523@blackbody.suse.cz>
 <Y+P17OVZZWVpYIb0@cmpxchg.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y+P17OVZZWVpYIb0@cmpxchg.org>
Precedence: bulk

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