Re: [PATCH v2 10/11] sched: move cfs task on a CPU with higher capacity

On Fri, May 23, 2014 at 05:53:04PM +0200, Vincent Guittot wrote:

@@ -7282,6 +7289,12 @@ static inline int nohz_kick_needed(struct rq *rq) if (nr_busy > 1) goto need_kick_unlock;

• if ((rq->cfs.h_nr_running >= 1)
  

•  && ((rq->cpu_power * sd->imbalance_pct) <
  

• 			(rq->cpu_power_orig * 100)))
  

• 	goto need_kick_unlock;
  

• }

sd = rcu_dereference(per_cpu(sd_asym, cpu));

So what happens when a cpu is consistently low on power (say due to a pinned RT task) the balancer would quickly adjust the load level, but this would endlessly kick things into action, even though we're balanced just fine.