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Commit 4dcfe102 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Avoid SMT siblings in select_idle_sibling() if possible 



Avoid select_idle_sibling() from picking a sibling thread if there's
an idle core that shares cache.

This fixes SMT balancing in the increasingly common case where there's
a shared cache core available to balance to.

Tested-by: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1321350377.1421.55.camel@twins


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent f1c6f1a7

kernel/sched_fair.c

+28 −14
Original line number Diff line number Diff line
@@ -2326,7 +2326,8 @@ static int select_idle_sibling(struct task_struct *p, int target) 
	int cpu = smp_processor_id();

	int prev_cpu = task_cpu(p);

	struct sched_domain *sd;

	int i;

	struct sched_group *sg;

	int i, smt = 0;



	/*

	 * If the task is going to be woken-up on this cpu and if it is
@@ -2346,25 +2347,38 @@ static int select_idle_sibling(struct task_struct *p, int target) 
	 * Otherwise, iterate the domains and find an elegible idle cpu.

	 */

	rcu_read_lock();

again:

	for_each_domain(target, sd) {

		if (!(sd->flags & SD_SHARE_PKG_RESOURCES))

			break;

		if (!smt && (sd->flags & SD_SHARE_CPUPOWER))

			continue;



		for_each_cpu_and(i, sched_domain_span(sd), tsk_cpus_allowed(p)) {

			if (idle_cpu(i)) {

				target = i;

		if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {

			if (!smt) {

				smt = 1;

				goto again;

			}

			break;

		}



		sg = sd->groups;

		do {

			if (!cpumask_intersects(sched_group_cpus(sg),

						tsk_cpus_allowed(p)))

				goto next;



			for_each_cpu(i, sched_group_cpus(sg)) {

				if (!idle_cpu(i))

					goto next;

			}



		/*

		 * Lets stop looking for an idle sibling when we reached

		 * the domain that spans the current cpu and prev_cpu.

		 */

		if (cpumask_test_cpu(cpu, sched_domain_span(sd)) &&

		    cpumask_test_cpu(prev_cpu, sched_domain_span(sd)))

			break;

			target = cpumask_first_and(sched_group_cpus(sg),

					tsk_cpus_allowed(p));

			goto done;

next:

			sg = sg->next;

		} while (sg != sd->groups);

	}

done:

	rcu_read_unlock();



	return target;