sched: Enable idle balance to pull single task towards cpu with higher capacity

We do not want to miss out on the ability to pull a single remaining
task from a potential source cpu towards an idle destination cpu. Add an
extra criteria to need_active_balance() to kick off active load balance
if the source cpu is over-utilized and has lower capacity than the
destination cpu.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 530cd573fa5debf28ff135cdaf22e82ff3c2fda7..8324c5e8f3ceadeea90af8887ead0b442ba70548 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8729,6 +8729,13 @@ static int need_active_balance(struct lb_env *env)
        if (env->src_grp_type == group_misfit_task)
                return 1;
 
+       if ((capacity_of(env->src_cpu) < capacity_of(env->dst_cpu)) &&
+                               env->src_rq->cfs.h_nr_running == 1 &&
+                               cpu_overutilized(env->src_cpu) &&
+                               !cpu_overutilized(env->dst_cpu)) {
+               return 1;
+       }
+
        return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
 }