Commit a0f03b61 authored by Mel Gorman's avatar Mel Gorman Committed by Ingo Molnar
Browse files

sched/numa: Stop an exhastive search if a reasonable swap candidate or idle CPU is found 



When domains are imbalanced or overloaded a search of all CPUs on the
target domain is searched and compared with task_numa_compare. In some
circumstances, a candidate is found that is an obvious win.

 o A task can move to an idle CPU and an idle CPU is found
 o A swap candidate is found that would move to its preferred domain

This patch terminates the search when either condition is met.

Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Hillf Danton <hdanton@sina.com>
Link: https://lore.kernel.org/r/20200224095223.13361-14-mgorman@techsingularity.net
parent 88cca72c

kernel/sched/fair.c

+27 −4
Original line number Diff line number Diff line
@@ -1707,7 +1707,7 @@ static bool load_too_imbalanced(long src_load, long dst_load, 
 * into account that it might be best if task running on the dst_cpu should

 * be exchanged with the source task

 */

static void task_numa_compare(struct task_numa_env *env,

static bool task_numa_compare(struct task_numa_env *env,

			      long taskimp, long groupimp, bool maymove)

{

	struct numa_group *cur_ng, *p_ng = deref_curr_numa_group(env->p);
@@ -1718,9 +1718,10 @@ static void task_numa_compare(struct task_numa_env *env, 
	int dist = env->dist;

	long moveimp = imp;

	long load;

	bool stopsearch = false;



	if (READ_ONCE(dst_rq->numa_migrate_on))

		return;

		return false;



	rcu_read_lock();

	cur = rcu_dereference(dst_rq->curr);
@@ -1731,8 +1732,10 @@ static void task_numa_compare(struct task_numa_env *env, 
	 * Because we have preemption enabled we can get migrated around and

	 * end try selecting ourselves (current == env->p) as a swap candidate.

	 */

	if (cur == env->p)

	if (cur == env->p) {

		stopsearch = true;

		goto unlock;

	}



	if (!cur) {

		if (maymove && moveimp >= env->best_imp)
@@ -1860,8 +1863,27 @@ assign: 
	}



	task_numa_assign(env, cur, imp);



	/*

	 * If a move to idle is allowed because there is capacity or load

	 * balance improves then stop the search. While a better swap

	 * candidate may exist, a search is not free.

	 */

	if (maymove && !cur && env->best_cpu >= 0 && idle_cpu(env->best_cpu))

		stopsearch = true;



	/*

	 * If a swap candidate must be identified and the current best task

	 * moves its preferred node then stop the search.

	 */

	if (!maymove && env->best_task &&

	    env->best_task->numa_preferred_nid == env->src_nid) {

		stopsearch = true;

	}

unlock:

	rcu_read_unlock();



	return stopsearch;

}



static void task_numa_find_cpu(struct task_numa_env *env,
@@ -1916,7 +1938,8 @@ static void task_numa_find_cpu(struct task_numa_env *env, 
			continue;



		env->dst_cpu = cpu;

		task_numa_compare(env, taskimp, groupimp, maymove);

		if (task_numa_compare(env, taskimp, groupimp, maymove))

			break;

	}

}

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