linux-kernel - Re: [PATCH 2/3] sched,numa: retry placement more frequently when misplaced

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Date:	Fri, 11 Apr 2014 10:46:57 -0700
From:	Joe Perches <joe@...ches.com>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	peterz@...radead.org, chegu_vinod@...com, mgorman@...e.de
Subject: Re: [PATCH 2/3] sched,numa: retry placement more frequently when
 misplaced

On Fri, 2014-04-11 at 13:00 -0400, riel@...hat.com wrote:
> This patch reduces the interval at which migration is retried,
> when the task's numa_scan_period is small.

More style trivia and a question.

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
[]
> @@ -1326,12 +1326,15 @@ static int task_numa_migrate(struct task_struct *p)
>  /* Attempt to migrate a task to a CPU on the preferred node. */
>  static void numa_migrate_preferred(struct task_struct *p)
>  {
> +	unsigned long interval = HZ;

Perhaps it'd be better without the unnecessary initialization.

>  	/* This task has no NUMA fault statistics yet */
>  	if (unlikely(p->numa_preferred_nid == -1 || !p->numa_faults_memory))
>  		return;
>  
>  	/* Periodically retry migrating the task to the preferred node */
> -	p->numa_migrate_retry = jiffies + HZ;
> +	interval = min(interval, msecs_to_jiffies(p->numa_scan_period) / 16);

and use

	interval = min_t(unsigned long, HZ,
			 msecs_to_jiffies(p->numa_scan_period) / 16);


btw; why 16?

Can msecs_to_jiffies(p->numa_scan_period) ever be < 16?


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