linux-kernel - Re: [PATCH 1/2] sched/numa: Stop an exhastive search if an idle core is found

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Message-ID: <20221024133435.e2kajx5k7jzznp25@suse.de>
Date:   Mon, 24 Oct 2022 14:34:35 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Hao Jia <jiahao.os@...edance.com>
Cc:     mingo@...hat.com, peterz@...radead.org, mingo@...nel.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        bristot@...hat.com, vschneid@...hat.com,
        mgorman@...hsingularity.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched/numa: Stop an exhastive search if an idle core
 is found

On Fri, Oct 21, 2022 at 02:15:57PM +0800, Hao Jia wrote:
> In update_numa_stats() we try to find an idle cpu on the NUMA node,
> preferably an idle core. When we find an idle core,
> we can stop searching.
> 
> Signed-off-by: Hao Jia <jiahao.os@...edance.com>
> ---
>  kernel/sched/fair.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e4a0b8bd941c..b7cbec539c77 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1792,7 +1792,7 @@ static void update_numa_stats(struct task_numa_env *env,
>  		ns->nr_running += rq->cfs.h_nr_running;
>  		ns->compute_capacity += capacity_of(cpu);
>  
> -		if (find_idle && !rq->nr_running && idle_cpu(cpu)) {
> +		if (find_idle && idle_core < 0 && !rq->nr_running && idle_cpu(cpu)) {
>  			if (READ_ONCE(rq->numa_migrate_on) ||
>  			    !cpumask_test_cpu(cpu, env->p->cpus_ptr))
>  				continue;
> @@ -1801,6 +1801,9 @@ static void update_numa_stats(struct task_numa_env *env,
>  				ns->idle_cpu = cpu;
>  
>  			idle_core = numa_idle_core(idle_core, cpu);
> +			/* If we find an idle core, stop searching. */
> +			if (idle_core >= 0)
> +				ns->idle_cpu = idle_core;
>  		}
>  	}
>  	rcu_read_unlock();
> @@ -1808,9 +1811,6 @@ static void update_numa_stats(struct task_numa_env *env,
>  	ns->weight = cpumask_weight(cpumask_of_node(nid));
>  
>  	ns->node_type = numa_classify(env->imbalance_pct, ns);
> -
> -	if (idle_core >= 0)
> -		ns->idle_cpu = idle_core;
>  }
>  

Remove the change in the first hunk and call break in the second hunk
after updating ns->idle_cpu.

-- 
Mel Gorman
SUSE Labs