linux-kernel - Re: [PATCH] sched/fair: Rearrange select_task_rq

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Date:   Tue, 24 Apr 2018 16:00:00 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Rearrange select_task_rq_fair() to optimize
 it

On 24-04-18, 11:02, Valentin Schneider wrote:
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index cacee15..ad09b67 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6613,7 +6613,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
>  static int
>  select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
>  {
> -	struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
> +	struct sched_domain *tmp, *sd = NULL;
>  	int cpu = smp_processor_id();
>  	int new_cpu = prev_cpu;
>  	int want_affine = 0;
> @@ -6636,8 +6636,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
>  		 */
>  		if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
>  		    cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
> +			if (cpu != prev_cpu)
> +				new_cpu = wake_affine(tmp, p, cpu, prev_cpu, sync);
> +
>  			sd = NULL; /* Prefer wake_affine over balance flags */
> -			affine_sd = tmp;
>  			break;
>  		}
>  
> @@ -6657,16 +6659,11 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
>  			sync_entity_load_avg(&p->se);
>  
>  		new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
> -	} else {
> -		if (affine_sd && cpu != prev_cpu)
> -			new_cpu = wake_affine(affine_sd, p, cpu, prev_cpu, sync);
> +	} else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
> +		new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
>  
> -		if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
> -			new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
> -
> -			if (want_affine)
> -				current->recent_used_cpu = cpu;
> -		}
> +		if (want_affine)
> +			current->recent_used_cpu = cpu;
>  	}
>  	rcu_read_unlock();

LGTM.

I will merge it as part of the current patch, but maybe wait for a few
days before sending V2.

-- 
viresh