linux-kernel - Re: [RFC PATCH v2] cgroup: Track time in cgroup v2 freezer

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Message-ID: <mknvbcalyaheobnfeeyyldytcoyturmeuq3twcrri5gaxtjojs@bbyqhshtjfab>
Date: Fri, 18 Jul 2025 10:20:18 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Tejun Heo <tj@...nel.org>
Cc: 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: [RFC PATCH v2] cgroup: Track time in cgroup v2 freezer

On Thu, Jul 17, 2025 at 07:05:14AM -1000, Tejun Heo <tj@...nel.org> wrote:
> I wonder what hierarchical summing would look like for this.

So do I.
Thus I meant to expose this only in a *.local file not the hierarchical
one.

But I realize it should [1] match cpu.stat[.local]:thottled_usec
since they're similar quantities in principle.
- cpu.stat:thottled_usec
  - sums the time the cgroup's quota was in effect
  - not hierarchical (:-/)
- cpu.stat.local:thottled_usec
  - not hierarchical
  - sums the time cgroup's or ancestor's quota was in effect
    -> IIUC this is what's the motivation of the original patch

HTH,
Michal

[1] I'd find it more logical if
cpu.stat:thottled_usec were cpu.stat.local:thottling_usec and
cpu.stat.local:thottled_usec were cpu.stat.local:throttled_usec.
Only to illustrate my understanding of hierarchy in cpu.stat, it doesn't
matter since it's what it is now.

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