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: <0064b782-2bed-4375-aba8-3745aa306a6d@huaweicloud.com>
Date: Wed, 23 Jul 2025 09:28:02 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Michal Koutný <mkoutny@...e.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 2025/7/22 19:54, Michal Koutný wrote:
> 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.
> 

This is what I worry about. Thank you for your confirmation.

Best regards,
Ridong