linux-kernel - Re: [RESEND PATCH v2] sched/fair: Remove check in idle_balance against migration

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Message-ID: <20180316143550.GH4064@hirez.programming.kicks-ass.net>
Date:   Fri, 16 Mar 2018 15:35:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Rohit Jain <rohit.k.jain@...cle.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        steven.sistare@...cle.com, joelaf@...gle.com, jbacik@...com,
        juri.lelli@...hat.com, dhaval.giani@...cle.com, efault@....de,
        riel@...riel.com
Subject: Re: [RESEND PATCH v2] sched/fair: Remove check in idle_balance
 against migration_cost

On Wed, Mar 14, 2018 at 11:36:47AM -0700, Rohit Jain wrote:
> Signed-off-by: Rohit Jain <rohit.k.jain@...cle.com>
> 
> Signed-off-by: Rohit Jain <rohit.k.jain@...cle.com>

Surely you only need a single on of those.

> ---
>  kernel/sched/fair.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5eb3ffc..569ea83 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8804,8 +8804,7 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
>  	 */
>  	rq_unpin_lock(this_rq, rf);
>  
> -	if (this_rq->avg_idle < sysctl_sched_migration_cost ||
> -	    !this_rq->rd->overload) {
> +	if (!this_rq->rd->overload) {
>  		rcu_read_lock();
>  		sd = rcu_dereference_check_sched_domain(this_rq->sd);
>  		if (sd)

I don't think that actually works right on the current tree. In
particular look at commit:

  31e77c93e432 ("sched/fair: Update blocked load when newly idle")