1 files changed, 57 insertions, 1 deletions

diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index c3e0652520a1..836e9b062e5e 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -257,6 +257,62 @@ show_one(sampling_down_factor, sampling_down_factor);
 show_one(ignore_nice_load, ignore_nice);
 show_one(powersave_bias, powersave_bias);
 
+/**
+ * update_sampling_rate - update sampling rate effective immediately if needed.
+ * @new_rate: new sampling rate
+ *
+ * If new rate is smaller than the old, simply updaing
+ * dbs_tuners_int.sampling_rate might not be appropriate. For example,
+ * if the original sampling_rate was 1 second and the requested new sampling
+ * rate is 10 ms because the user needs immediate reaction from ondemand
+ * governor, but not sure if higher frequency will be required or not,
+ * then, the governor may change the sampling rate too late; up to 1 second
+ * later. Thus, if we are reducing the sampling rate, we need to make the
+ * new value effective immediately.
+ */
+static void update_sampling_rate(unsigned int new_rate)
+{
+        int cpu;
+
+        dbs_tuners_ins.sampling_rate = new_rate
+                                     = max(new_rate, min_sampling_rate);
+
+        for_each_online_cpu(cpu) {
+                struct cpufreq_policy *policy;
+                struct cpu_dbs_info_s *dbs_info;
+                unsigned long next_sampling, appointed_at;
+
+                policy = cpufreq_cpu_get(cpu);
+                if (!policy)
+                        continue;
+                dbs_info = &per_cpu(od_cpu_dbs_info, policy->cpu);
+                cpufreq_cpu_put(policy);
+
+                mutex_lock(&dbs_info->timer_mutex);
+
+                if (!delayed_work_pending(&dbs_info->work)) {
+                        mutex_unlock(&dbs_info->timer_mutex);
+                        continue;
+                }
+
+                next_sampling  = jiffies + usecs_to_jiffies(new_rate);
+                appointed_at = dbs_info->work.timer.expires;
+
+
+                if (time_before(next_sampling, appointed_at)) {
+
+                        mutex_unlock(&dbs_info->timer_mutex);
+                        cancel_delayed_work_sync(&dbs_info->work);
+                        mutex_lock(&dbs_info->timer_mutex);
+
+                        schedule_delayed_work_on(dbs_info->cpu, &dbs_info->work,
+                                                 usecs_to_jiffies(new_rate));
+
+                }
+                mutex_unlock(&dbs_info->timer_mutex);
+        }
+}
+
 static ssize_t store_sampling_rate(struct kobject *a, struct attribute *b,
                                    const char *buf, size_t count)
 {
@@ -265,7 +321,7 @@ static ssize_t store_sampling_rate(struct kobject *a, struct attribute *b,
         ret = sscanf(buf, "%u", &input);
         if (ret != 1)
                 return -EINVAL;
-        dbs_tuners_ins.sampling_rate = max(input, min_sampling_rate);
+        update_sampling_rate(input);
         return count;
 }