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

[Joshua Hahn]

> From: Tao Cui <cuitao@xxxxxxxxxx>
> 
> 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".
> 
> nice_usec was added by commit aefa398d93d5 ("cgroup/rstat: Tracking
> cgroup-level niced CPU time") and core_sched.force_idle_usec by commit
> 1fcf54deb767 ("sched/core: add forced idle accounting for cgroups"); the
> documentation was not updated in either case.
> 
> Update the cpu.stat description to list both fields and fix the count.
> 
> Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>

Hello Tao, thank you for the patch! I should have updated this when
I added the nice stats. Thank you for finding this and updating it.

> ---
>  Documentation/admin-guide/cgroup-v2.rst | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 0df15a672cf3..778b759dd892 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1144,12 +1144,18 @@ will be referred to. All time durations are in microseconds.
>  	A read-only flat-keyed file.
>  	This file exists whether the controller is enabled or not.
>  
> -	It always reports the following three stats, which account for all the
> +	It always reports the following four stats, which account for all the
>  	processes in the cgroup (including those in descendant cgroups):

I have to ask, which tree is this based on? I can't seem to find a single
tree that contains the "(including those in descendant cgroups)" section
anywhere. 

>  	- usage_usec
>  	- user_usec
>  	- system_usec
> +	- nice_usec
> +
> +	When core scheduling (CONFIG_SCHED_CORE) is enabled, an additional
> +	stat is reported:
> +
> +	- core_sched.force_idle_usec
>  
>  	and the following five when the controller is enabled, which account for
>  	only the processes under the fair-class scheduler:
> -- 
> 2.43.0

Otherwise, the change looks good. I just wanted to know what it was based
on, in case I'm missing something. Thanks, have a great day!
Joshua