linux-kernel - Re: [PATCH 6/6] sched/numa: Delay retrying placement for automatic NUMA balance after wake

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Message-ID: <20180213140137.GN25201@hirez.programming.kicks-ass.net>
Date:   Tue, 13 Feb 2018 15:01:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] sched/numa: Delay retrying placement for automatic
 NUMA balance after wake_affine

On Tue, Feb 13, 2018 at 01:37:30PM +0000, Mel Gorman wrote:
> +static void
> +update_wa_numa_placement(struct task_struct *p, int prev_cpu, int target)
> +{
> +	unsigned long interval;
> +
> +	if (!static_branch_likely(&sched_numa_balancing))
> +		return;
> +
> +	/* If balancing has no preference then continue gathering data */
> +	if (p->numa_preferred_nid == -1)
> +		return;
> +
> +	/*
> +	 * If the wakeup is not affecting locality then it is neutral from
> +	 * the perspective of NUMA balacing so continue gathering data.
> +	 */
> +	if (cpus_share_cache(prev_cpu, target))
> +		return;

Dang, I wanted to mention this before, but it slipped my mind. The
comment and code don't match.

Did you want to write:

	if (cpu_to_node(prev_cpu) == cpu_to_node(target))
		return;

> +	/*
> +	 * Temporarily prevent NUMA balancing trying to place waker/wakee after
> +	 * wakee has been moved by wake_affine. This will potentially allow
> +	 * related tasks to converge and update their data placement. The
> +	 * 4 * numa_scan_period is to allow the two-pass filter to migrate
> +	 * hot data to the wakers node.
> +	 */
> +	interval = max(sysctl_numa_balancing_scan_delay,
> +			 p->numa_scan_period << 2);
> +	p->numa_migrate_retry = jiffies + msecs_to_jiffies(interval);
> +
> +	interval = max(sysctl_numa_balancing_scan_delay,
> +			 current->numa_scan_period << 2);
> +	current->numa_migrate_retry = jiffies + msecs_to_jiffies(interval);
> +}