linux-kernel - Re: [PATCH 5/8] sched: Favour moving tasks towards the preferred node

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Date:	Fri, 28 Jun 2013 22:44:27 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/8] sched: Favour moving tasks towards the preferred node

> > Yes, I understand that numa should have more priority over cache.
> > But the schedstats will not be updated about whether the task was hot or
> > cold.
> > 
> > So lets say the task was cache hot but numa wants it to move, then we
> > should certainly move it but we should update the schedstats to mention that we
> > moved a cache hot task.
> > 
> > Something akin to this.
> > 
> > 	tsk_cache_hot = task_hot(p, env->src_rq->clock_task, env->sd);
> > 	if (tsk_cache_hot) {
> > 		if (migrate_improves_locality(p, env) || 
> > 		 	(env->sd->nr_balance_failed > env->sd->cache_nice_tries)) {
> > #ifdef CONFIG_SCHEDSTATS
> > 			schedstat_inc(env->sd, lb_hot_gained[env->idle]);
> > 			schedstat_inc(p, se.statistics.nr_forced_migrations);
> > #endif
> > 			return 1;
> > 		}
> > 		schedstat_inc(p, se.statistics.nr_failed_migrations_hot);
> > 		return 0;
> > 	}
> > 	return 1;
> > 
> 
> Thanks. Is this acceptable?
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b3848e0..c3a153e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4088,8 +4088,13 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
>  	 * 3) too many balance attempts have failed.
>  	 */
> 
> -	if (migrate_improves_locality(p, env))
> +	if (migrate_improves_locality(p, env)) {
> +#ifdef CONFIG_SCHEDSTATS
> +		schedstat_inc(env->sd, lb_hot_gained[env->idle]);
> +		schedstat_inc(p, se.statistics.nr_forced_migrations);
> +#endif
>  		return 1;
> +	}
> 

In this case, we account even cache cold threads as _cache hot_ in
schedstats.

We need the task_hot() call to determine if task is cache hot or not.
So the migrate_improves_locality(), I think should be called within the
tsk_cache_hot check.

Do you have issues with the above snippet that I posted earlier?

>  	tsk_cache_hot = task_hot(p, env->src_rq->clock_task, env->sd);
>  	if (!tsk_cache_hot)
> 
> -- 
> Mel Gorman
> SUSE Labs
> 

-- 
Thanks and Regards
Srikar Dronamraju

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