linux-kernel - Re: cpu.stat in core or cpu controller (was Re: [RFC PATCH v2] cgroup: Track time in cgroup v2 freezer)

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Message-ID: <aHvHb0i6c8A_aCIo@slm.duckdns.org>
Date: Sat, 19 Jul 2025 06:27:27 -1000
From: Tejun Heo <tj@...nel.org>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: Michal Koutný <mkoutny@...e.com>,
	Tiffany Yang <ynaffit@...gle.com>, linux-kernel@...r.kernel.org,
	John Stultz <jstultz@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Boyd <sboyd@...nel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Pavel Machek <pavel@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Chen Ridong <chenridong@...wei.com>, kernel-team@...roid.com,
	Jonathan Corbet <corbet@....net>, cgroups@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: cpu.stat in core or cpu controller (was Re: [RFC PATCH v2]
 cgroup: Track time in cgroup v2 freezer)

On Sat, Jul 19, 2025 at 10:01:07AM +0800, Chen Ridong wrote:
...
> What I'm considering is moving the implementation of cpu.stat from cgroup_base_files to
> cpu_cgrp_subsys—without changing the user-facing interface (filenames and content remain the same).
> However, the interface would only appear if the CPU subsystem is enabled.
> 
> Currently, cpu.stat and cpu.stat.local are visible in every cgroup, even when the CPU subsystem is
> disabled. The only populated fields in such cases are:
> 
> - usage_usec
> - user_usec
> - system_usec
> - nice_usec
> 
> I’m unsure whether this change would be acceptable?

I don't think so and don't really see what benefits moving the stats would
bring. Why would we move these?

Thanks.

-- 
tejun