[PATCH v4 08/20] sched/fair: load balance only among preferred CPUs

[Shrikanth Hegde <sshegde@linux.ibm.com>]

Consider only preferred CPUs for load balance.

With this, load balance will end up choosing a preferred CPUs for pull.
This makes it not fight against the push task mechanism which happens
at tick. Also, this stops active balance to happen on non-preferred CPU
pulling the load.

This means there is no load balancing if the task is pinned only to
non-preferred CPUs. They will continue to run where they were previously
running before the CPUs was marked as non-preferred.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 kernel/sched/fair.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d78467ec6ee1..3f3c7f0ca489 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -13291,6 +13291,9 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq,
 
 	cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask);
 
+	/* Spread load among preferred CPUs */
+	cpumask_and(cpus, cpus, cpu_preferred_mask);
+
 	schedstat_inc(sd->lb_count[idle]);
 
 redo:
-- 
2.47.3