ondemand governor automatic downscaling

@@ -34,13 +34,9 @@
  */
 
 #define DEF_FREQUENCY_UP_THRESHOLD		(80)
-#define MIN_FREQUENCY_UP_THRESHOLD		(0)
+#define MIN_FREQUENCY_UP_THRESHOLD		(10)
 #define MAX_FREQUENCY_UP_THRESHOLD		(100)
 
-#define DEF_FREQUENCY_DOWN_THRESHOLD		(20)
-#define MIN_FREQUENCY_DOWN_THRESHOLD		(0)
-#define MAX_FREQUENCY_DOWN_THRESHOLD		(100)
-
 /* 
  * The polling frequency of this governor depends on the capability of 
  * the processor. Default polling frequency is 1000 times the transition

@@ -78,12 +74,10 @@ struct dbs_tuners {
 	unsigned int 		sampling_rate;
 	unsigned int		sampling_down_factor;
 	unsigned int		up_threshold;
-	unsigned int		down_threshold;
 };
 
 static struct dbs_tuners dbs_tuners_ins = {
 	.up_threshold 		= DEF_FREQUENCY_UP_THRESHOLD,
-	.down_threshold 	= DEF_FREQUENCY_DOWN_THRESHOLD,
 	.sampling_down_factor 	= DEF_SAMPLING_DOWN_FACTOR,
 };
 

@@ -115,7 +109,6 @@ static ssize_t show_##file_name						\
 show_one(sampling_rate, sampling_rate);
 show_one(sampling_down_factor, sampling_down_factor);
 show_one(up_threshold, up_threshold);
-show_one(down_threshold, down_threshold);
 
 static ssize_t store_sampling_down_factor(struct cpufreq_policy *unused, 
 		const char *buf, size_t count)

@@ -161,8 +154,7 @@ static ssize_t store_up_threshold(struct
 
 	down(&dbs_sem);
 	if (ret != 1 || input > MAX_FREQUENCY_UP_THRESHOLD || 
-			input < MIN_FREQUENCY_UP_THRESHOLD ||
-			input <= dbs_tuners_ins.down_threshold) {
+			input < MIN_FREQUENCY_UP_THRESHOLD) {
 		up(&dbs_sem);
 		return -EINVAL;
 	}

@@ -173,26 +165,6 @@ static ssize_t store_up_threshold(struct
 	return count;
 }
 
-static ssize_t store_down_threshold(struct cpufreq_policy *unused, 
-		const char *buf, size_t count)
-{
-	unsigned int input;
-	int ret;
-	ret = sscanf (buf, "%u", &input);
-
-	down(&dbs_sem);
-	if (ret != 1 || input > MAX_FREQUENCY_DOWN_THRESHOLD || 
-			input < MIN_FREQUENCY_DOWN_THRESHOLD ||
-			input >= dbs_tuners_ins.up_threshold) {
-		up(&dbs_sem);
-		return -EINVAL;
-	}
-
-	dbs_tuners_ins.down_threshold = input;
-	up(&dbs_sem);
-
-	return count;
-}
 
 #define define_one_rw(_name) \
 static struct freq_attr _name = \

@@ -201,7 +173,6 @@ __ATTR(_name, 0644, show_##_name, store_
 define_one_rw(sampling_rate);
 define_one_rw(sampling_down_factor);
 define_one_rw(up_threshold);
-define_one_rw(down_threshold);
 
 static struct attribute * dbs_attributes[] = {
 	&sampling_rate_max.attr,

@@ -209,7 +180,6 @@ static struct attribute * dbs_attributes
 	&sampling_rate.attr,
 	&sampling_down_factor.attr,
 	&up_threshold.attr,
-	&down_threshold.attr,
 	NULL
 };
 

@@ -222,8 +192,8 @@ static struct attribute_group dbs_attr_g
 
 static void dbs_check_cpu(int cpu)
 {
-	unsigned int idle_ticks, up_idle_ticks, down_idle_ticks;
-	unsigned int freq_down_step;
+	unsigned int idle_ticks, up_idle_ticks, total_ticks;
+	unsigned int freq_next;
 	unsigned int freq_down_sampling_rate;
 	static int down_skip[NR_CPUS];
 	struct cpu_dbs_info_s *this_dbs_info;

@@ -290,7 +261,12 @@ static void dbs_check_cpu(int cpu)
 	down_skip[cpu]++;
 	if (down_skip[cpu] < dbs_tuners_ins.sampling_down_factor)
 		return;
+	down_skip[cpu] = 0;
 
+	/* don't try to decrease the frequency if it's already the min */
+	if (policy->cur == policy->min)
+		return;
+	
 	idle_ticks = UINT_MAX;
 	for_each_cpu_mask(j, policy->cpus) {
 		unsigned int tmp_idle_ticks, total_idle_ticks;

@@ -308,27 +285,23 @@ static void dbs_check_cpu(int cpu)
 			idle_ticks = tmp_idle_ticks;
 	}
 
-	/* Scale idle ticks by 100 and compare with up and down ticks */
-	idle_ticks *= 100;
-	down_skip[cpu] = 0;
-
+	/* Compute how many ticks there are between two measurements */
 	freq_down_sampling_rate = dbs_tuners_ins.sampling_rate *
 		dbs_tuners_ins.sampling_down_factor;
-	down_idle_ticks = (100 - dbs_tuners_ins.down_threshold) *
-			sampling_rate_in_HZ(freq_down_sampling_rate);
-
-	if (idle_ticks > down_idle_ticks) {
-		freq_down_step = (5 * policy->max) / 100;
-
-		/* max freq cannot be less than 100. But who knows.... */
-		if (unlikely(freq_down_step == 0))
-			freq_down_step = 5;
+	total_ticks = sampling_rate_in_HZ(freq_down_sampling_rate);
+	
+	/* 
+	 * The optimal frequency is the frequency that is the lowest that
+	 * can support the current CPU usage without triggering 
+	 * the up policy. To be safe, we focus 10 points under the threshold.
+	 */
+	freq_next = ((total_ticks - idle_ticks) * 100 * policy->cur) /
+	       		(total_ticks * (dbs_tuners_ins.up_threshold - 10));
 
+	if (freq_next <= ((policy->cur * 95) / 100))
 		__cpufreq_driver_target(policy,
-			policy->cur - freq_down_step, 
-			CPUFREQ_RELATION_H);
-		return;
-	}
+			freq_next, 
+			CPUFREQ_RELATION_L);
 }
 
 static void do_dbs_timer(void *data)