[RFCv5 PATCH 34/46] sched: Enable idle balance to pull single task towards cpu with higher capacity

Morten Rasmussen
2015-07-07T18:25:38Z

From: Dietmar Eggemann <dietmar.eggemann@arm.com>

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 if the
energy aware system operates above the tipping point.

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>
---
kernel/sched/fair.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 48ecf02..97eb83e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7569,6 +7569,13 @@ static int need_active_balance(struct lb_env *env)
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);
}

@@ -7923,7 +7930,8 @@ static int idle_balance(struct rq *this_rq)
this_rq->idle_stamp = rq_clock(this_rq);

if (this_rq->avg_idle < sysctl_sched_migration_cost ||
- !this_rq->rd->overload) {
+ (!energy_aware() && !this_rq->rd->overload) ||
+ (energy_aware() && !this_rq->rd->overutilized)) {
rcu_read_lock();
sd = rcu_dereference_check_sched_domain(this_rq->sd);
if (sd)
--
1.9.1