[RFCv5 PATCH 35/46] sched: Disable energy-unfriendly nohz kicks

Morten Rasmussen
2015-07-07T18:25:49Z

With energy-aware scheduling enabled nohz_kick_needed() generates many
nohz idle-balance kicks which lead to nothing when multiple tasks get
packed on a single cpu to save energy. This causes unnecessary wake-ups
and hence wastes energy. Make these conditions depend on !energy_aware()
for now until the energy-aware nohz story gets sorted out.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
kernel/sched/fair.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 97eb83e..8e0cbd4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8424,12 +8424,13 @@ static inline bool nohz_kick_needed(struct rq *rq)
if (time_before(now, nohz.next_balance))
return false;

- if (rq->nr_running >= 2)
+ if (rq->nr_running >= 2 &&
+ (!energy_aware() || cpu_overutilized(cpu)))
return true;

rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_busy, cpu));
- if (sd) {
+ if (sd && !energy_aware()) {
sgc = sd->groups->sgc;
nr_busy = atomic_read(&sgc->nr_busy_cpus);

--
1.9.1