Re: [PATCH] cgroup/cpu: document cpu.stat nice_usec and core_sched.force_idle_usec

[Tao Cui <cui.tao@linux.dev>]

在 2026/7/20 23:26, Michal Koutný 写道:
> On Sat, Jul 18, 2026 at 04:01:00PM +0800, Tao Cui <cui.tao@linux.dev> wrote:
>> From: Tao Cui <cuitao@kylinos.cn>
>>
>> cgroup_base_stat_cputime_show() unconditionally prints a fourth base
>> stat, nice_usec, in addition to usage_usec/user_usec/system_usec, and
>> also prints core_sched.force_idle_usec when CONFIG_SCHED_CORE is enabled.
>> Neither field is currently described in the cpu.stat section of
>> cgroup-v2.rst, which still states it "always reports the following three
>> stats".
> 
> Just to better sense popularity of the fields -- have you found this out
> by:
> a) reading cpu.stat and being confused about semantics of the fields or
> b) scanning files/code vs docs looking for discrepancies?
> 
(b). I found it while auditing the cgroup cpu controller, comparing
what cgroup_base_stat_cputime_show() prints against the cpu.stat docs.
nice_usec is emitted unconditionally but not listed there, and the
"three stats" count was stale.

The audit is groundwork for a prototype daemon that monitors
per-cgroup resource usage and adjusts limits dynamically. The design
is inspired by DAMON, but DAMON targets a single resource domain,
whereas container workloads need coordinated control across several
(cpu, memory, io) — which is why I'm going through the per-controller
stat interfaces.

Thanks,
Tao
> Thanks,
> Michal