linux-kernel - Re: [RFC PATCH 10/23] sched/fair: Use classes of tasks when selecting a busiest runqueue

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Message-ID: <YzLdxS3dXCHq+bLa@hirez.programming.kicks-ass.net>
Date:   Tue, 27 Sep 2022 13:25:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, "Tim C . Chen" <tim.c.chen@...el.com>
Subject: Re: [RFC PATCH 10/23] sched/fair: Use classes of tasks when
 selecting a busiest runqueue

On Fri, Sep 09, 2022 at 04:11:52PM -0700, Ricardo Neri wrote:

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 7368a0b453ee..085b1f75d90b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10009,6 +10009,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
>  	int i;
>  
>  	for_each_cpu_and(i, sched_group_span(group), env->cpus) {
> +		int busiest_class_delta_score = INT_MIN;

You sure you want to break ties toward a negative IPC 'improvement' ?

>  		unsigned long capacity, load, util;
>  		unsigned int nr_running;
>  		enum fbq_type rt;
> @@ -10118,6 +10119,20 @@ static struct rq *find_busiest_queue(struct lb_env *env,
>  			if (busiest_nr < nr_running) {
>  				busiest_nr = nr_running;
>  				busiest = rq;
> +			} else if (sched_task_classes_enabled() &&
> +				   busiest_nr == nr_running) {
> +				int curr_class_delta_score;
> +
> +				curr_class_delta_score = arch_get_task_class_score(rq->curr->class,
> +										   env->dst_cpu) -
> +							 arch_get_task_class_score(rq->curr->class,
> +										   cpu_of(rq));

*sigh*, you really couldn't find a more ugly layout if you tried.

Perhaps use less than novella length identifiers?

> +
> +				if (busiest_class_delta_score < curr_class_delta_score) {
> +					busiest_class_delta_score = curr_class_delta_score;
> +					busiest_nr = nr_running;
> +					busiest = rq;
> +				}
>  			}
>  			break;