linux-kernel - Re: [PATCH 4/4] sched,fair: Fix PELT integrity for new tasks

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Date:	Mon, 20 Jun 2016 11:52:14 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Yuyang Du <yuyang.du@...el.com>, Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Benjamin Segall <bsegall@...gle.com>,
	Paul Turner <pjt@...gle.com>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 4/4] sched,fair: Fix PELT integrity for new tasks

On Mon, Jun 20, 2016 at 11:23:39AM +0200, Vincent Guittot wrote:

> > @@ -738,7 +739,20 @@ void post_init_entity_util_avg(struct sc
> >  		sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
> >  	}
> >  
> > -	update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, false);
> > +	if (entity_is_task(se)) {
> 
> Why only task ?

Only tasks can be of another class, the cgroup se's must be fair.

> > +		struct task_struct *p = task_of(se);
> > +		if (p->sched_class != &fair_sched_class) {
> > +			/*
> > +			 * For !fair tasks do attach_entity_load_avg()
> > +			 * followed by detach_entity_load_avg() as per
> > +			 * switched_from_fair().
> > +			 */
> > +			se->avg.last_update_time = now;
> > +			return;
> > +		}
> > +	}
> > +
> > +	update_cfs_rq_load_avg(now, cfs_rq, false);
> >  	attach_entity_load_avg(cfs_rq, se);
> 
> Don't we have to do a complete attach with attach_task_cfs_rq instead
> of just the load_avg ? to set also depth ?

init_tg_cfs_entity() sets depth for cgroup entities,
attach_task_cfs_rq() reset depth on switched_to().

So that should be fine.

> ---
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -723,6 +723,7 @@ void post_init_entity_util_avg(struct sched_entity *se)
>  	struct cfs_rq *cfs_rq = cfs_rq_of(se);
>  	struct sched_avg *sa = &se->avg;
>  	long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;
> +	u64 now = cfs_rq_clock_task(cfs_rq);
>  
>  	if (cap > 0) {
>  		if (cfs_rq->avg.util_avg != 0) {
> @@ -737,8 +738,18 @@ void post_init_entity_util_avg(struct sched_entity *se)
>  		sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
>  	}
>  
> -	update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, false);
> -	attach_entity_load_avg(cfs_rq, se);

There is no p here...

> +	if (p->sched_class == &fair_sched_class) {
> +		/* fair entity must be attached to cfs_rq */
> +		attach_task_cfs_rq(se);
> +	} else {
> +		/*
> +		 * For !fair tasks do attach_entity_load_avg()
> +		 * followed by detach_entity_load_avg() as per
> +		 * switched_from_fair().
> +		 */
> +		se->avg.last_update_time = now;
> +	}
> +
>  }

And you're now not attaching new cgroup thingies.