+static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle)
+{
+ struct rq *this_rq = cpu_rq(this_cpu);
+ struct rq *rq;
+ int balance_cpu;
+
+ if (idle != CPU_IDLE || !this_rq->nohz_balance_kick)
+ return;
+
+ for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
+ if (balance_cpu == this_cpu)
+ continue;
+
+ /*
+ * If this cpu gets work to do, stop the load balancing
+ * work being done for other cpus. Next load
+ * balancing owner will pick it up.
+ */
+ if (need_resched()) {
+ this_rq->nohz_balance_kick = 0;
+ break;
+ }
+
+ raw_spin_lock_irq(&this_rq->lock);
+ update_rq_clock(this_rq);
+ update_cpu_load(this_rq);
+ raw_spin_unlock_irq(&this_rq->lock);
+
+ rebalance_domains(balance_cpu, CPU_IDLE);
+
+ rq = cpu_rq(balance_cpu);
+ if (time_after(this_rq->next_balance, rq->next_balance))
+ this_rq->next_balance = rq->next_balance;
+ }
+ nohz.next_balance = this_rq->next_balance;
+ this_rq->nohz_balance_kick = 0;
+}
+
+/*
+ * Current heuristic for kicking the idle load balancer
+ * - first_pick_cpu is the one of the busy CPUs. It will kick
+ * idle load balancer when it has more than one process active. This
+ * eliminates the need for idle load balancing altogether when we have
+ * only one running process in the system (common case).
+ * - If there are more than one busy CPU, idle load balancer may have
+ * to run for active_load_balance to happen (i.e., two busy CPUs are
+ * SMT or core siblings and can run better if they move to different
+ * physical CPUs). So, second_pick_cpu is the second of the busy CPUs
+ * which will kick idle load balancer as soon as it has any load.
+ */
+static inline int nohz_kick_needed(struct rq *rq, int cpu)
+{
+ unsigned long now = jiffies;
+ int ret;
+ int first_pick_cpu, second_pick_cpu;
+
+ if (time_before(now, nohz.next_balance))
+ return 0;
+
+ if (!rq->nr_running)
+ return 0;
+
+ first_pick_cpu = atomic_read(&nohz.first_pick_cpu);
+ second_pick_cpu = atomic_read(&nohz.second_pick_cpu);
+
+ if (first_pick_cpu < nr_cpu_ids && first_pick_cpu != cpu &&
+ second_pick_cpu < nr_cpu_ids && second_pick_cpu != cpu)
+ return 0;
+
+ ret = atomic_cmpxchg(&nohz.first_pick_cpu, nr_cpu_ids, cpu);
+ if (ret == nr_cpu_ids || ret == cpu) {
+ atomic_cmpxchg(&nohz.second_pick_cpu, cpu, nr_cpu_ids);
+ if (rq->nr_running > 1)
+ return 1;
+ } else {
+ ret = atomic_cmpxchg(&nohz.second_pick_cpu, nr_cpu_ids, cpu);
+ if (ret == nr_cpu_ids || ret == cpu) {
+ if (rq->nr_running)
+ return 1;
+ }
+ }
+ return 0;
+}
+#else
+static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle) { }
+#endif
+
+/*
+ * run_rebalance_domains is triggered when needed from the scheduler tick.
+ * Also triggered for nohz idle balancing (with nohz_balancing_kick set).
+ */