linux-kernel - Re: [PATCH 4/2] sched/cpupri: Add CPUPRI

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Date:   Tue, 20 Oct 2020 09:37:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/2] sched/cpupri: Add CPUPRI_HIGHER

On Mon, Oct 19, 2020 at 04:15:01PM +0200, Dietmar Eggemann wrote:
> On 14/10/2020 21:54, Peter Zijlstra wrote:
> > 
> > Add CPUPRI_HIGHER above the RT99 priority to denote the CPU is in use
> > by higher priority tasks (specifically deadline).
> 
> sugov:X already triggers this now on our !fast-switching devices running
> schedutil.

Right, that would also be a nice test-case for:

> > XXX: we should probably drive PUSH-PULL from cpupri, that would
> > automagically result in an RT-PUSH when DL sets cpupri to CPUPRI_HIGHER.

This, once we get there..

> > @@ -54,6 +56,10 @@ static int convert_prio(int prio)
> 
> The BUG_ON could be tightened:
> 
> -       BUG_ON(prio >= MAX_PRIO);
> +       BUG_ON(prio > MAX_RT_PRIO);
> 

Maybe I've not had enough wake-up juice, but I can't seem to locate
this.

> >  	case MAX_RT_PRIO-1:
> >  		cpupri = CPUPRI_NORMAL;		/*  0 */
> >  		break;
> > +
> > +	case MAX_RT_PRIO:
> > +		cpupri = CPUPRI_HIGHER;		/* 100 */
> > +		break;
> >  	}
> > 
> >  	return cpupri;
> 
> Just saw that the comment for cpupri_set() needs changing:
> 
> @@ -205,7 +208,7 @@ int cpupri_find_fitness(struct cpupri *cp, struct
> task_struct *p,
>   * cpupri_set - update the CPU priority setting
>   * @cp: The cpupri context
>   * @cpu: The target CPU
> - * @newpri: The priority (INVALID-RT99) to assign to this CPU
> + * @newpri: The priority (INVALID-RT1-RT99-NORMAL-HIGHER) to assign to
> this CPU

I made that:

+ * @newpri: The priority (INVALID,NORMAL,RT1-RT99,HIGHER) to assign to this CPU

> 
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>

Thanks!