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Commit e02e60c1 authored by Joonsoo Kim's avatar Joonsoo Kim Committed by Ingo Molnar
Browse files

sched: Prevent to re-select dst-cpu in load_balance() 



Commit 88b8dac0 makes load_balance() consider other cpus in its
group. But, in that, there is no code for preventing to
re-select dst-cpu. So, same dst-cpu can be selected over and
over.

This patch add functionality to load_balance() in order to
exclude cpu which is selected once. We prevent to re-select
dst_cpu via env's cpus, so now, env's cpus is a candidate not
only for src_cpus, but also dst_cpus.

With this patch, we can remove lb_iterations and
max_lb_iterations, because we decide whether we can go ahead or
not via env's cpus.

Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: default avatarJason Low <jason.low2@hp.com>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1366705662-3587-7-git-send-email-iamjoonsoo.kim@lge.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent e6252c3e

kernel/sched/fair.c

+15 −18
Original line number Diff line number Diff line
@@ -3905,7 +3905,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) 
		return 0;



	if (!cpumask_test_cpu(env->dst_cpu, tsk_cpus_allowed(p))) {

		int new_dst_cpu;

		int cpu;



		schedstat_inc(p, se.statistics.nr_failed_migrations_affine);
@@ -3920,12 +3920,15 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) 
		if (!env->dst_grpmask || (env->flags & LBF_SOME_PINNED))

			return 0;



		new_dst_cpu = cpumask_first_and(env->dst_grpmask,

						tsk_cpus_allowed(p));

		if (new_dst_cpu < nr_cpu_ids) {

		/* Prevent to re-select dst_cpu via env's cpus */

		for_each_cpu_and(cpu, env->dst_grpmask, env->cpus) {

			if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) {

				env->flags |= LBF_SOME_PINNED;

			env->new_dst_cpu = new_dst_cpu;

				env->new_dst_cpu = cpu;

				break;

			}

		}



		return 0;

	}
@@ -5008,7 +5011,6 @@ static int load_balance(int this_cpu, struct rq *this_rq, 
			int *balance)

{

	int ld_moved, cur_ld_moved, active_balance = 0;

	int lb_iterations, max_lb_iterations;

	struct sched_group *group;

	struct rq *busiest;

	unsigned long flags;
@@ -5028,15 +5030,8 @@ static int load_balance(int this_cpu, struct rq *this_rq, 
	 * For NEWLY_IDLE load_balancing, we don't need to consider

	 * other cpus in our group

	 */

	if (idle == CPU_NEWLY_IDLE) {

	if (idle == CPU_NEWLY_IDLE)

		env.dst_grpmask = NULL;

		/*

		 * we don't care max_lb_iterations in this case,

		 * in following patch, this will be removed

		 */

		max_lb_iterations = 0;

	} else

		max_lb_iterations = cpumask_weight(env.dst_grpmask);



	cpumask_copy(cpus, cpu_active_mask);
@@ -5064,7 +5059,6 @@ redo: 
	schedstat_add(sd, lb_imbalance[idle], env.imbalance);



	ld_moved = 0;

	lb_iterations = 1;

	if (busiest->nr_running > 1) {

		/*

		 * Attempt to move tasks. If find_busiest_group has found
@@ -5121,14 +5115,17 @@ more_balance: 
		 * moreover subsequent load balance cycles should correct the

		 * excess load moved.

		 */

		if ((env.flags & LBF_SOME_PINNED) && env.imbalance > 0 &&

				lb_iterations++ < max_lb_iterations) {

		if ((env.flags & LBF_SOME_PINNED) && env.imbalance > 0) {



			env.dst_rq	 = cpu_rq(env.new_dst_cpu);

			env.dst_cpu	 = env.new_dst_cpu;

			env.flags	&= ~LBF_SOME_PINNED;

			env.loop	 = 0;

			env.loop_break	 = sched_nr_migrate_break;



			/* Prevent to re-select dst_cpu via env's cpus */

			cpumask_clear_cpu(env.dst_cpu, env.cpus);



			/*

			 * Go back to "more_balance" rather than "redo" since we

			 * need to continue with same src_cpu.