[RFC][PATCH 4/9] sched: Make periodic load-balance disregard cpus with a cpu_power of 1

[Morten Rasmussen <morten.rasmussen@arm.com>]

Some of the load_balance() helper functions will put tasks on cpus with
cpu_power=1 when they are completely idle. This patch changes this behaviour.

The patch is a quick fix. The load_balance() helper functions should be
revisited to implement proper handling of cpus with cpu_power=1.

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
CC: Ingo Molnar <mingo@kernel.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Catalin Marinas <catalin.marinas@arm.com>
---
 kernel/sched/fair.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f637ea5..4610463 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3952,6 +3952,13 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
 	}
 
 	/*
+	 * Vacate cpus disabled by the power scheduler even if the cache is
+	 * hot
+	 */
+	if (!power_cpu_balance(env->src_cpu))
+		return 1;
+
+	/*
 	 * Aggressive migration if:
 	 * 1) task is cache cold, or
 	 * 2) too many balance attempts have failed.
@@ -4500,6 +4507,11 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 			update_group_power(env->sd, env->dst_cpu);
 		} else if (time_after_eq(jiffies, group->sgp->next_update))
 			update_group_power(env->sd, env->dst_cpu);
+
+		if (!power_cpu_balance(env->dst_cpu)) {
+			*balance = 0;
+			return;
+		}
 	}
 
 	/* Adjust by relative CPU power of the group */
-- 
1.7.9.5