[PATCH] cpufreq_conservative: aligning of codebase with ondemand

Since the conservative govenor was released its codebase has drifted from the
the direction and updates that have been applied to the ondemand govornor.

This patch addresses the lack of updates in that period and brings
conservative back up to date.  The resulting diff file between
cpufreq_ondemand.c and cpufreq_conservative.c is now much smaller and shows
more clearly the differences between the two.

Another reason to do this is ages ago, knowingly, I did a piss poor attempt
at making conservative less responsive by knocking up
DEF_SAMPLING_RATE_LATENCY_MULTIPLIER by two orders of magnitude.  I did fix
this ages ago but in my dis-organisation I must have toasted the diff and
left it the way it was.  About two weeks ago a user contacted me saying he
was having problems with the conservative governor with his AMD Athlon XP-M
2800+ as /sys/devices/system/cpu/cpu0/cpufreq/conservative showed
  sampling_rate_min   9950000
  sampling_rate_max   1360065408

Nine seconds to decide about changing the frequency....not too responsive :)

Signed-off-by: Alexander Clouter <alex-kernel@digriz.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

drivers/cpufreq/cpufreq_conservative.c

@@ -35,12 +35,7 @@
  */
 
 #define DEF_FREQUENCY_UP_THRESHOLD		(80)
-#define MIN_FREQUENCY_UP_THRESHOLD		(0)
-#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 
@@ -53,10 +48,14 @@
  * All times here are in uS.
  */
 static unsigned int 				def_sampling_rate;
-#define MIN_SAMPLING_RATE			(def_sampling_rate / 2)
+#define MIN_SAMPLING_RATE_RATIO			(2)
+/* for correct statistics, we need at least 10 ticks between each measure */
+#define MIN_STAT_SAMPLING_RATE			(MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
+#define MIN_SAMPLING_RATE			(def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
 #define MAX_SAMPLING_RATE			(500 * def_sampling_rate)
-#define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER	(100000)
-#define DEF_SAMPLING_DOWN_FACTOR		(5)
+#define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER	(1000)
+#define DEF_SAMPLING_DOWN_FACTOR		(1)
+#define MAX_SAMPLING_DOWN_FACTOR		(10)
 #define TRANSITION_LATENCY_LIMIT		(10 * 1000)
 
 static void do_dbs_timer(void *data);
@@ -136,7 +135,7 @@ static ssize_t store_sampling_down_factor(struct cpufreq_policy *unused,
 	unsigned int input;
 	int ret;
 	ret = sscanf (buf, "%u", &input);
-	if (ret != 1 )
+	if (ret != 1 || input > MAX_SAMPLING_DOWN_FACTOR || input < 1)
 		return -EINVAL;
 
 	mutex_lock(&dbs_mutex);
@@ -173,8 +172,7 @@ static ssize_t store_up_threshold(struct cpufreq_policy *unused,
 	ret = sscanf (buf, "%u", &input);
 
 	mutex_lock(&dbs_mutex);
-	if (ret != 1 || input > MAX_FREQUENCY_UP_THRESHOLD || 
-			input < MIN_FREQUENCY_UP_THRESHOLD ||
+	if (ret != 1 || input > 100 || input < 0 ||
 			input <= dbs_tuners_ins.down_threshold) {
 		mutex_unlock(&dbs_mutex);
 		return -EINVAL;
@@ -194,8 +192,7 @@ static ssize_t store_down_threshold(struct cpufreq_policy *unused,
 	ret = sscanf (buf, "%u", &input);
 
 	mutex_lock(&dbs_mutex);
-	if (ret != 1 || input > MAX_FREQUENCY_DOWN_THRESHOLD || 
-			input < MIN_FREQUENCY_DOWN_THRESHOLD ||
+	if (ret != 1 || input > 100 || input < 0 ||
 			input >= dbs_tuners_ins.up_threshold) {
 		mutex_unlock(&dbs_mutex);
 		return -EINVAL;
@@ -337,7 +334,6 @@ static void dbs_check_cpu(int cpu)
 	 */
 
 	/* Check for frequency increase */
-
 	idle_ticks = UINT_MAX;
 	for_each_cpu_mask(j, policy->cpus) {
 		unsigned int tmp_idle_ticks, total_idle_ticks;
@@ -357,7 +353,7 @@ static void dbs_check_cpu(int cpu)
 	/* Scale idle ticks by 100 and compare with up and down ticks */
 	idle_ticks *= 100;
 	up_idle_ticks = (100 - dbs_tuners_ins.up_threshold) *
-		usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
+			usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
 
 	if (idle_ticks < up_idle_ticks) {
 		down_skip[cpu] = 0;
@@ -398,6 +394,7 @@ static void dbs_check_cpu(int cpu)
 		struct cpu_dbs_info_s *j_dbs_info;
 
 		j_dbs_info = &per_cpu(cpu_dbs_info, j);
+		/* Check for frequency decrease */
 		total_idle_ticks = j_dbs_info->prev_cpu_idle_up;
 		tmp_idle_ticks = total_idle_ticks -
 			j_dbs_info->prev_cpu_idle_down;
@@ -414,12 +411,14 @@ static void dbs_check_cpu(int cpu)
 	freq_down_sampling_rate = dbs_tuners_ins.sampling_rate *
 		dbs_tuners_ins.sampling_down_factor;
 	down_idle_ticks = (100 - dbs_tuners_ins.down_threshold) *
-			usecs_to_jiffies(freq_down_sampling_rate);
+		usecs_to_jiffies(freq_down_sampling_rate);
 
 	if (idle_ticks > down_idle_ticks) {
-		/* if we are already at the lowest speed then break out early
+		/*
+		 * if we are already at the lowest speed then break out early
 		 * or if we 'cannot' reduce the speed as the user might want
-		 * freq_step to be zero */
+		 * freq_step to be zero
+		 */
 		if (requested_freq[cpu] == policy->min
 				|| dbs_tuners_ins.freq_step == 0)
 			return;
@@ -434,9 +433,8 @@ static void dbs_check_cpu(int cpu)
 		if (requested_freq[cpu] < policy->min)
 			requested_freq[cpu] = policy->min;
 
-		__cpufreq_driver_target(policy,
-			requested_freq[cpu],
-			CPUFREQ_RELATION_H);
+		__cpufreq_driver_target(policy, requested_freq[cpu],
+				CPUFREQ_RELATION_H);
 		return;
 	}
 }
@@ -507,13 +505,16 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
 		if (dbs_enable == 1) {
 			unsigned int latency;
 			/* policy latency is in nS. Convert it to uS first */
+			latency = policy->cpuinfo.transition_latency / 1000;
+			if (latency == 0)
+				latency = 1;
 
-			latency = policy->cpuinfo.transition_latency;
-			if (latency < 1000)
-				latency = 1000;
-
-			def_sampling_rate = (latency / 1000) *
+			def_sampling_rate = latency *
 					DEF_SAMPLING_RATE_LATENCY_MULTIPLIER;
+
+			if (def_sampling_rate < MIN_STAT_SAMPLING_RATE)
+				def_sampling_rate = MIN_STAT_SAMPLING_RATE;
+
 			dbs_tuners_ins.sampling_rate = def_sampling_rate;
 			dbs_tuners_ins.ignore_nice = 0;
 			dbs_tuners_ins.freq_step = 5;