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: <7746e963-1c2d-402b-9a28-1554a34e096a@huaweicloud.com>
Date: Fri, 25 Jul 2025 09:54:33 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Tejun Heo <tj@...nel.org>
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 2025/7/25 9:08, Tejun Heo wrote:
> 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.
> 

Thank you Tj, This is clear now.

Best regards,
Ridong