On Fri, Jun 28, 2013 at 03:37:23PM +0530, Srikar Dronamraju wrote:
> > > > +
> > > > +
> > > > /*
> > > > * can_migrate_task - may task p from runqueue rq be migrated to
> > > > this_cpu?
> > > > */
> > > > @@ -3945,10 +3977,14 @@ int can_migrate_task(struct task_struct *p,
> > > > struct lb_env *env)
> > > >
> > > > /*
> > > > * Aggressive migration if:
> > > > - * 1) task is cache cold, or
> > > > - * 2) too many balance attempts have failed.
> > > > + * 1) destination numa is preferred
> > > > + * 2) task is cache cold, or
> > > > + * 3) too many balance attempts have failed.
> > > > */
> > > >
> > > > + if (migrate_improves_locality(p, env))
> > > > + return 1;
> > >
> > > Shouldnt this be under tsk_cache_hot check?
> > >
> > > If the task is cache hot, then we would have to update the corresponding
> > > schedstat
> > > metrics.
> >
> > No; you want migrate_degrades_locality() to be like task_hot(). You want
> > to _always_ migrate tasks towards better locality irrespective of local
> > cache hotness.
> >
>
> 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;
Ah right.. ok that might make sense.
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