linux-kernel - Re: [PATCH 2/2] cgroup, docs: Document interaction of RT processes with cpu controller

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Message-ID: <d259ba35-a4a5-4e01-b539-85f2080fdd33@redhat.com>
Date: Wed, 5 Mar 2025 09:16:15 -0500
From: Waiman Long <llong@...hat.com>
To: shashank.mahadasyam@...y.com, Tejun Heo <tj@...nel.org>,
 Johannes Weiner <hannes@...xchg.org>, Michal Koutný
 <mkoutny@...e.com>, Jonathan Corbet <corbet@....net>
Cc: cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, Shinya Takumi <shinya.takumi@...y.com>
Subject: Re: [PATCH 2/2] cgroup, docs: Document interaction of RT processes
 with cpu controller


On 3/4/25 11:12 PM, Shashank Balaji via B4 Relay wrote:
> From: Shashank Balaji <shashank.mahadasyam@...y.com>
>
> If the cpu controller is enabled in a CONFIG_RT_GROUP_SCHED
> disabled setting, cpu.stat and cpu.pressure account for realtime
> processes, and cpu.uclamp.{min, max} affect realtime processes as well.
> None of the other interface files are affected by or affect realtime
> processes.
>
> Signed-off-by: Shashank Balaji <shashank.mahadasyam@...y.com>
> ---
>   Documentation/admin-guide/cgroup-v2.rst | 18 +++++++++++++-----
>   1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index f293a13b42ed69e7c6bf5e974cb86e228411af4e..2c267f42e5fef9c4e2c3530ce73330d680b9b2dc 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1095,7 +1095,9 @@ realtime processes irrespective of CONFIG_RT_GROUP_SCHED.
>   CPU Interface Files
>   ~~~~~~~~~~~~~~~~~~~
>   
> -All time durations are in microseconds.
> +All time durations are in microseconds. Only cpu.stat and cpu.pressure account
> +for realtime processes, and only cpu.uclamp.min and cpu.uclamp.max
> +affect realtime processes.
>   
>     cpu.stat
>   	A read-only flat-keyed file.
> @@ -1115,6 +1117,9 @@ All time durations are in microseconds.
>   	- nr_bursts
>   	- burst_usec
>   
> +    The runtime of realtime processes is accounted for only by the usage_usec,
> +	user_usec, and system_usec fields.
> +

Alignment problem!

Anyway, I am not familiar enough with these cpu control files to give a 
review yet.

Cheers,
Longman

>     cpu.weight
>   	A read-write single value file which exists on non-root
>   	cgroups.  The default is "100".
> @@ -1158,8 +1163,9 @@ All time durations are in microseconds.
>     cpu.pressure
>   	A read-write nested-keyed file.
>   
> -	Shows pressure stall information for CPU. See
> -	:ref:`Documentation/accounting/psi.rst <psi>` for details.
> +	Shows pressure stall information for CPU, including the contribution of
> +	realtime processes. See :ref:`Documentation/accounting/psi.rst <psi>`
> +	for details.
>   
>     cpu.uclamp.min
>           A read-write single value file which exists on non-root cgroups.
> @@ -1170,7 +1176,8 @@ All time durations are in microseconds.
>   
>           This interface allows reading and setting minimum utilization clamp
>           values similar to the sched_setattr(2). This minimum utilization
> -        value is used to clamp the task specific minimum utilization clamp.
> +        value is used to clamp the task specific minimum utilization clamp,
> +        including those of realtime processes.
>   
>           The requested minimum utilization (protection) is always capped by
>           the current value for the maximum utilization (limit), i.e.
> @@ -1185,7 +1192,8 @@ All time durations are in microseconds.
>   
>           This interface allows reading and setting maximum utilization clamp
>           values similar to the sched_setattr(2). This maximum utilization
> -        value is used to clamp the task specific maximum utilization clamp.
> +        value is used to clamp the task specific maximum utilization clamp,
> +        including those of realtime processes.
>   
>     cpu.idle
>   	A read-write single value file which exists on non-root cgroups.
>