On 29 May 2014 16:04, Peter Zijlstra <pet...@infradead.org> wrote: > 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.
If there is more than 1 running task or more than 1 busy CPU, we will kick the ilb because of the former conditions. Then, if there is only 1 task and no other busy cpu, we should trig the ILB. Nevertheless, I can add a test to check that there is an idle cpu in the sched_domain -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
