Re: [PATCH 16/19] sched/numa: Detect if node actively handling migration

[Rik van Riel <riel@surriel.com>]

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On Mon, 2018-06-04 at 15:30 +0530, Srikar Dronamraju wrote:

> @@ -1554,6 +1562,9 @@ static void task_numa_compare(struct
> task_numa_env *env,
>  	if (READ_ONCE(dst_rq->numa_migrate_on))
>  		return;
>  
> +	if (*move && READ_ONCE(pgdat->active_node_migrate))
> +		*move = false;

Why not do this check in task_numa_find_cpu?

That way you won't have to pass this in as a
pointer, and you also will not have to recalculate
NODE_DATA(cpu_to_node(env->dst_cpu)) for every CPU.

>  	/*
> +	 * If the numa importance is less than SMALLIMP,

              ^^^ numa improvement

> +	 * task migration might only result in ping pong
> +	 * of tasks and also hurt performance due to cache
> +	 * misses.
> +	 */
> +	if (imp < SMALLIMP || imp <= env->best_imp + SMALLIMP / 2)
> +		goto unlock;

I can see a use for the first test, but why limit the
search for the best score once you are past the
threshold?

I don't understand the use for that second test.

What workload benefits from it?

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