On Thu, Jan 15, 2015 at 11:09:30AM +0100, Vincent Guittot wrote:
As a sidenote, this will note generate more spurious ilb because we already
s/note/not/
trig an ilb if there is more than 1 busy cpu. If this cpu is the only one that has a task, we will trig the ilb once for migrating the task.
+static inline bool nohz_kick_needed(struct rq *rq) { unsigned long now = jiffies; struct sched_domain *sd; struct sched_group_capacity *sgc; int nr_busy, cpu = rq->cpu;
- bool kick = false;
if (unlikely(rq->idle_balance))
return false;/*
- We may be recently in ticked or tickless idle mode. At the first
@@ -7472,38 +7498,44 @@ static inline int nohz_kick_needed(struct rq *rq) * balancing. */ if (likely(!atomic_read(&nohz.nr_cpus)))
return false;if (time_before(now, nohz.next_balance))
return false;if (rq->nr_running >= 2)
return true;
So this,
rcu_read_lock(); sd = rcu_dereference(per_cpu(sd_busy, cpu)); if (sd) { sgc = sd->groups->sgc; nr_busy = atomic_read(&sgc->nr_busy_cpus);
if (nr_busy > 1) {kick = true;goto unlock;}- }
- sd = rcu_dereference(rq->sd);
- if (sd) {
if ((rq->cfs.h_nr_running >= 1) &&check_cpu_capacity(rq, sd)) {kick = true;goto unlock;}- }
vs this: how would we ever get here?
If h_nr_running > 1, must then not nr_running > 1 as well?
- sd = rcu_dereference(per_cpu(sd_asym, cpu)); if (sd && (cpumask_first_and(nohz.idle_cpus_mask, sched_domain_span(sd)) < cpu))
kick = true;
For consistencies sake I would've added a goto unlock here as well.
+unlock: rcu_read_unlock();
- return kick;
}