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

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Message-ID: <20130628174445.GP8362@linux.vnet.ibm.com>
Date:	Fri, 28 Jun 2013 23:14:45 +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

> > > 
> > > -	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?
> > 
> 
> The migrate_improves_locality call had already happened so it cannot be
> true after the tsk_cache_hot check is made so I was confused. If the call is
> moved within task cache hot then it changes the intent of the patch because

Yes,  I was suggesting moving it inside.

> cache hotness then trumps memory locality which is not intended. Memory
> locality is expected to trump cache hotness.
> 

But whether the memory locality trumps or the cache hotness, the result
would still be the same but a little concise code.

> How about this?
> 
>         tsk_cache_hot = task_hot(p, env->src_rq->clock_task, env->sd);
> 
>         if (migrate_improves_locality(p, env)) {
> #ifdef CONFIG_SCHEDSTATS
>                 if (tsk_cache_hot) {
>                         schedstat_inc(env->sd, lb_hot_gained[env->idle]);
>                         schedstat_inc(p, se.statistics.nr_forced_migrations);
>                 }
> #endif
>                 return 1;
>         }
> 
>         if (!tsk_cache_hot ||
>                 env->sd->nr_balance_failed > env->sd->cache_nice_tries) {
> #ifdef CONFIG_SCHEDSTATS
>                 if (tsk_cache_hot) {
>                         schedstat_inc(env->sd, lb_hot_gained[env->idle]);
>                         schedstat_inc(p, se.statistics.nr_forced_migrations);
>                 }
> #endif
>                 return 1;
>         }

Yes, this looks fine to me.
> 

-- 
Thanks and Regards
Srikar Dronamraju

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