@@ -25,9 +25,12 @@
 #include <linux/tick.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
+#include <linux/cpu.h>
 
 #include "cpufreq_governor.h"
 
+static DEFINE_PER_CPU(struct dbs_data *, cpu_cur_dbs);
+
 static inline u64 get_cpu_idle_time_jiffy(unsigned int cpu, u64 *wall)
 {
 	u64 idle_time;

@@ -185,6 +188,46 @@ static inline void dbs_timer_exit(struct cpu_dbs_common_info *cdbs)
 	cancel_delayed_work_sync(&cdbs->work);
 }
 
+static int __cpuinit cpu_callback(struct notifier_block *nfb,
+		unsigned long action, void *hcpu)
+{
+	unsigned int cpu = (unsigned long)hcpu;
+	struct device *cpu_dev = get_cpu_device(cpu);
+	struct dbs_data *dbs_data = per_cpu(cpu_cur_dbs, cpu);
+	struct cpu_dbs_common_info *cpu_cdbs = dbs_data->get_cpu_cdbs(cpu);
+	unsigned int sampling_rate;
+
+	if (dbs_data->governor == GOV_CONSERVATIVE) {
+		struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
+		sampling_rate = cs_tuners->sampling_rate;
+	} else {
+		struct od_dbs_tuners *od_tuners = dbs_data->tuners;
+		sampling_rate = od_tuners->sampling_rate;
+	}
+
+	if (cpu_dev) {
+		switch (action) {
+		case CPU_ONLINE:
+		case CPU_ONLINE_FROZEN:
+		case CPU_DOWN_FAILED:
+		case CPU_DOWN_FAILED_FROZEN:
+			dbs_timer_init(dbs_data, cpu_cdbs,
+					sampling_rate, cpu);
+			break;
+		case CPU_DOWN_PREPARE:
+		case CPU_DOWN_PREPARE_FROZEN:
+			dbs_timer_exit(cpu_cdbs);
+			break;
+		}
+	}
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block __refdata ondemand_cpu_notifier = {
+	.notifier_call = cpu_callback,
+};
+
 int cpufreq_governor_dbs(struct dbs_data *dbs_data,
 		struct cpufreq_policy *policy, unsigned int event)
 {

@@ -296,7 +339,11 @@ second_time:
 				j_cdbs = dbs_data->get_cpu_cdbs(j);
 				dbs_timer_init(dbs_data, j_cdbs,
 					       *sampling_rate, j);
+
+				per_cpu(cpu_cur_dbs, j) = dbs_data;
 			}
+
+			register_hotcpu_notifier(&ondemand_cpu_notifier);
 		} else {
 			dbs_timer_init(dbs_data, cpu_cdbs, *sampling_rate, cpu);
 		}

@@ -307,11 +354,15 @@ second_time:
 			cs_dbs_info->enable = 0;
 
 		if (dbs_sw_coordinated_cpus(cpu_cdbs)) {
+			unregister_hotcpu_notifier(&ondemand_cpu_notifier);
+
 			for_each_cpu(j, policy->cpus) {
 				struct cpu_dbs_common_info *j_cdbs;
 
 				j_cdbs = dbs_data->get_cpu_cdbs(j);
 				dbs_timer_exit(j_cdbs);
+
+				per_cpu(cpu_cur_dbs, j) = NULL;
 			}
 		} else {
 			dbs_timer_exit(cpu_cdbs);