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

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Message-ID: <sgwmpdabmhcu3h7yxxjq3x4n6hk6p4m5bsopimfbmt46lokj7k@c4oood4anage>
Date: Wed, 2 Apr 2025 14:49:37 +0200
From: Michal Koutný <mkoutny@...e.com>
To: "Shashank.Mahadasyam@...y.com" <Shashank.Mahadasyam@...y.com>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Jonathan Corbet <corbet@....net>, Waiman Long <longman@...hat.com>, 
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Shinya.Takumi@...y.com" <Shinya.Takumi@...y.com>
Subject: Re: [PATCH 2/2] cgroup, docs: Document interaction of RT processes
 with cpu controller

Hello.

On Fri, Mar 28, 2025 at 10:45:02AM +0000, "Shashank.Mahadasyam@...y.com" <Shashank.Mahadasyam@...y.com> wrote:
> Given the different scheduling classes (fair, ext, rt, deadline), it would be nice
> to document which cpu interface files are related to which scheduling classes.
> Like, cpu.idle applies to only the fair class, cpu.weight applies to the fair class,
> as well as ext, if configured so, cpu.stat accounts for all classes
> (I'm not sure about this, I haven't tested this yet), etc.
> 
> The proposed patch is in this direction, but just for the rt class. Any suggestions
> on how this intent can be made clearer? How about something like this:

Classes are implementation terminology but userspace knows this under
scheduling policies (SCHED_NORMAL,..., SCHED_EXT). It might be better to
use that categories.

> 
> CPU Interface Files
> ~~~~~~~~~~~~~~~~~~~
> 
> All time durations are in microseconds. The scheduling classes mentioned beside
> the interface files are the only classes they are related to.

list of related <categories> is only indicative as implementation may change

(Even when talking about policies I think the relation still tends to be
an implementation detail, so I'd also add something like the above. But
I think it's good to have such an overview to know what is where
implemented.)

HTH,
Michal

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