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Commit c1ceac62 authored by Rik van Riel's avatar Rik van Riel Committed by Ingo Molnar
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sched/numa: Reduce conflict between fbq_classify_rq() and migration 



It is possible for fbq_classify_rq() to indicate that a CPU has tasks that
should be moved to another NUMA node, but for migrate_improves_locality
and migrate_degrades_locality to not identify those tasks.

This patch always gives preference to preferred node evaluations, and
only checks the number of faults when evaluating moves between two
non-preferred nodes on a larger NUMA system.

On a two node system, the number of faults is never evaluated. Either
a task is about to be pulled off its preferred node, or migrated onto
it.

Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: mgorman@suse.de
Link: http://lkml.kernel.org/r/20150514225936.35b91717@annuminas.surriel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 80ed87c8

kernel/sched/fair.c

+33 −27
Original line number Diff line number Diff line
@@ -5663,10 +5663,15 @@ static int task_hot(struct task_struct *p, struct lb_env *env) 
}



#ifdef CONFIG_NUMA_BALANCING

/* Returns true if the destination node has incurred more faults */

/*

 * Returns true if the destination node is the preferred node.

 * Needs to match fbq_classify_rq(): if there is a runnable task

 * that is not on its preferred node, we should identify it.

 */

static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env)

{

	struct numa_group *numa_group = rcu_dereference(p->numa_group);

	unsigned long src_faults, dst_faults;

	int src_nid, dst_nid;



	if (!sched_feat(NUMA_FAVOUR_HIGHER) || !p->numa_faults ||
@@ -5680,29 +5685,30 @@ static bool migrate_improves_locality(struct task_struct *p, struct lb_env *env) 
	if (src_nid == dst_nid)

		return false;



	if (numa_group) {

		/* Task is already in the group's interleave set. */

		if (node_isset(src_nid, numa_group->active_nodes))

			return false;



		/* Task is moving into the group's interleave set. */

		if (node_isset(dst_nid, numa_group->active_nodes))

			return true;



		return group_faults(p, dst_nid) > group_faults(p, src_nid);

	}



	/* Encourage migration to the preferred node. */

	if (dst_nid == p->numa_preferred_nid)

		return true;



	return task_faults(p, dst_nid) > task_faults(p, src_nid);

	/* Migrating away from the preferred node is bad. */

	if (src_nid == p->numa_preferred_nid)

		return false;



	if (numa_group) {

		src_faults = group_faults(p, src_nid);

		dst_faults = group_faults(p, dst_nid);

	} else {

		src_faults = task_faults(p, src_nid);

		dst_faults = task_faults(p, dst_nid);

	}



	return dst_faults > src_faults;

}





static bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env)

{

	struct numa_group *numa_group = rcu_dereference(p->numa_group);

	unsigned long src_faults, dst_faults;

	int src_nid, dst_nid;



	if (!sched_feat(NUMA) || !sched_feat(NUMA_RESIST_LOWER))
@@ -5717,23 +5723,23 @@ static bool migrate_degrades_locality(struct task_struct *p, struct lb_env *env) 
	if (src_nid == dst_nid)

		return false;



	if (numa_group) {

		/* Task is moving within/into the group's interleave set. */

		if (node_isset(dst_nid, numa_group->active_nodes))

			return false;



		/* Task is moving out of the group's interleave set. */

		if (node_isset(src_nid, numa_group->active_nodes))

	/* Migrating away from the preferred node is bad. */

	if (src_nid == p->numa_preferred_nid)

		return true;



		return group_faults(p, dst_nid) < group_faults(p, src_nid);

	}

	/* Encourage migration to the preferred node. */

	if (dst_nid == p->numa_preferred_nid)

		return false;



	/* Migrating away from the preferred node is always bad. */

	if (src_nid == p->numa_preferred_nid)

		return true;

	if (numa_group) {

		src_faults = group_faults(p, src_nid);

		dst_faults = group_faults(p, dst_nid);

	} else {

		src_faults = task_faults(p, src_nid);

		dst_faults = task_faults(p, dst_nid);

	}



	return task_faults(p, dst_nid) < task_faults(p, src_nid);

	return dst_faults < src_faults;

}



#else