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: <adrjkqsqqwxcsdr5z4wmxcrvgvutkulzgka6pjjv23v6242txr@vv2ysb46nhpk>
Date: Tue, 22 Jul 2025 13:54:07 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: Tejun Heo <tj@...nel.org>, 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 Tue, Jul 22, 2025 at 05:01:50PM +0800, Chen Ridong <chenridong@...weicloud.com> wrote:
> Specifically, this change would allow us to:
> 
> 1.Remove these CPU-specific callbacks from the core:
>   css_extra_stat_show()
>   css_local_stat_show()
> 2. Clean up the 'is_self' logic in rstat.c.

If you see an option to organize the code better, why not. (At the same
time, I currently also don't see the "why.)


> 3. Make the stat handling consistent across subsystems (currently cpu.stat is the only
> subsystem-specific stat implemented in the core).

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.

Michal

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