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: <aILZDyD4mPkiMrfd@slm.duckdns.org>
Date: Thu, 24 Jul 2025 15:08:31 -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 Wed, Jul 23, 2025 at 09:28:02AM +0800, Chen Ridong wrote:
> > But beware that the possibility of having cpu.stat without enabling the
> > cpu controller on v2 is a user visible behavior and I'm quite sure some
> > userspace relies on it, so you'd need to preserve that.
> 
> This is what I worry about. Thank you for your confirmation.

Yeah, this was an intentional decision - sacrificing a bit of code org
cleanliness for everyday usefulness. Enabling CPU controller can have
substantial overhead and having cpu stats available by default doesn't cost
much while improving usefulness.

Thanks.

-- 
tejun