linux-kernel - Re: [RFC 6/6] sched/fair: Add sched group latency support

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Date:   Mon, 21 Mar 2022 07:24:07 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, linux-kernel@...r.kernel.org, parth@...ux.ibm.com,
        qais.yousef@....com, chris.hyser@...cle.com,
        pkondeti@...eaurora.org, valentin.schneider@....com,
        patrick.bellasi@...bug.net, David.Laight@...lab.com,
        pjt@...gle.com, pavel@....cz, dhaval.giani@...cle.com,
        qperret@...gle.com, tim.c.chen@...ux.intel.com
Subject: Re: [RFC 6/6] sched/fair: Add sched group latency support

Hello,

On Fri, Mar 11, 2022 at 05:14:06PM +0100, Vincent Guittot wrote:
> Tasks can set its latency priority which is then used to decide to preempt
> the current running entity of the cfs but sched group entities still have
> the default latency priority.
> 
> Add a latency field in task group to set the latency priority of the group
> which will be used against other entity in the parent cfs.

One thing that bothers me about this interface is that the configuration
values aren't well defined. We have the same problems with the nice levels
but at least have them map to well defined weight values, which likely won't
change in any foreseeable future. The fact that we have the
not-too-well-defined nice levels as an interface shouldn't be a reason we
add another one. Provided that this is something scheduler folks want, it'd
be really great if the interface can be better thought through. What are the
numbers actually encoding?

Thanks.

-- 
tejun