[PATCH] cpufreq_ondemand

[Alexander Clouter <alex-kernel@digriz.org.uk>]

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Hi all,

After playing with the cpufreq_ondemand governor (many thanks to those whom 
made it) I made a number of alterations which suit me at least.  Really 
looking for feedback and of course once people have fixed any bugs they find 
and made the code look neater, possible inclusion?

The improvements (well I think they are) I have made:

1. I have replaced the algoritm it used to one which calculates the number of
	cpu idle cycles that have passed and compares it to the number of cpu
	cycles it would have expected to pass (for, the defaults, 20%/80%)

	this means a couple of divisions have been removed, which is always 
	nice and it lead to clearer code (for me at least), that was 
	until I added the handful of 'if' conditionals though.... :-/

2. controllable through 
	/sys/.../ondemand/ignore_nice, you can tell it to consider 'nice' 
	time as also idle cpu cycles.  Set it to '1' to treat 'nice' as cpu 
	in an active state.

3. (major) the scaling up and down of the cpufreq is now smoother.  I found 
	it really nasty that if it tripped < 20% idle time that the freq was 
	set to 100%.  This code smoothly increases the cpufreq as well as 
	doing a better job of decreasing it too

4. (minor) I changed DEF_SAMPLING_RATE_LATENCY_MULTIPLIER to 50000 and
	DEF_SAMPLING_DOWN_FACTOR to 5 as I found the defaults a bit annoying 
	on my system and resulted in the cpufreq constantly jumping.

	For my patch it works far better if the sampling rate is much lower 
	anyway, which can only be good for cpu efficiency in the long run

5. the grainity of how much cpufreq is increased or decreased is controlled 
	with sending a percentage to /sys/.../ondemand/freq_step_percent

6. debugging (with 'watch -n1 cat /sys/.../ondemand/requested_freq') and 
	backwards 'compatibility' to act like the 'userspace' governor is 
	avaliable with /sys/.../ondemand/requested_freq if 
	'freq_step_percent' is set to zero

7. there are extra checks to not bother to try increasing/decreasing the 
	cpufreq if there is nothing to do, or even can be done as it might 
	already be at min/max (or freq_step_percent is zero)

The code seems to work for me fine.  This is my first patch and the first 
thing I have really posted here so be gentle with me :)

Comments and improvements are of course more than welcome.

Of course full thanks go to all the original authors, my C coding is naff and 
I would of not been able to do this if it was not for the pretty much 
complete (for my needs) cpufreq_ondemand module; Venkatesh did say we could 
rip out the core algorithm and replace it with our own easily, he was right 
:)

Cheers

Alex

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diff -u -U 2 -r -N -d linux-2.6.9-rc4.orig/drivers/cpufreq/cpufreq_ondemand.c linux-2.6.9-rc4/drivers/cpufreq/cpufreq_ondemand.c
--- linux-2.6.9-rc4.orig/drivers/cpufreq/cpufreq_ondemand.c	2004-10-11 03:58:49.000000000 +0100
+++ linux-2.6.9-rc4/drivers/cpufreq/cpufreq_ondemand.c	2004-10-17 18:32:28.000000000 +0100
@@ -56,8 +56,8 @@
 static unsigned int 				def_sampling_rate;
 #define MIN_SAMPLING_RATE			(def_sampling_rate / 2)
 #define MAX_SAMPLING_RATE			(500 * def_sampling_rate)
-#define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER	(1000)
-#define DEF_SAMPLING_DOWN_FACTOR		(10)
+#define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER	(50000)
+#define DEF_SAMPLING_DOWN_FACTOR		(5)
 #define TRANSITION_LATENCY_LIMIT		(10 * 1000)
 #define sampling_rate_in_HZ(x)			(((x * HZ) < (1000 * 1000))?1:((x * HZ) / (1000 * 1000)))
 
@@ -65,8 +65,8 @@
 
 struct cpu_dbs_info_s {
 	struct cpufreq_policy 	*cur_policy;
-	unsigned int 		prev_cpu_idle_up;
-	unsigned int 		prev_cpu_idle_down;
+	unsigned int 		prev_cpu_ticks;
+	unsigned int		prev_cpu_idle_ticks;
 	unsigned int 		enable;
 };
 static DEFINE_PER_CPU(struct cpu_dbs_info_s, cpu_dbs_info);
@@ -81,6 +81,9 @@
 	unsigned int		sampling_down_factor;
 	unsigned int		up_threshold;
 	unsigned int		down_threshold;
+	unsigned int		requested_freq;
+	unsigned int		freq_step_percent;
+	unsigned int		ignore_nice;
 };
 
 struct dbs_tuners dbs_tuners_ins = {
@@ -116,6 +119,22 @@
 {									\
 	return sprintf(buf, "%u\n", dbs_tuners_ins.object);		\
 }
+
+static ssize_t show_requested_freq(struct cpufreq_policy *policy, char *buf)
+{
+	return sprintf (buf, "%u\n", dbs_tuners_ins.requested_freq);
+}
+
+static ssize_t show_freq_step_percent(struct cpufreq_policy *policy, char *buf)
+{
+	return sprintf (buf, "%u\n", dbs_tuners_ins.freq_step_percent);
+}
+
+static ssize_t show_ignore_nice(struct cpufreq_policy *policy, char *buf)
+{
+	return sprintf (buf, "%u\n", dbs_tuners_ins.ignore_nice);
+}
+
 show_one(sampling_rate, sampling_rate);
 show_one(sampling_down_factor, sampling_down_factor);
 show_one(up_threshold, up_threshold);
@@ -189,6 +208,63 @@
 	return count;
 }
 
+static ssize_t store_ignore_nice(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 ) {
+		if ( input > 1 )
+			input = 1;
+		dbs_tuners_ins.ignore_nice = input;
+	}
+	up(&dbs_sem);
+	return count;
+}
+
+static ssize_t store_freq_step_percent(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 ) {
+		/* someone might find 'freq_step_percent = 0' useful so this is
+		 * why I have added support to manually set the freq also; I
+		 * guess this would then permit a userland tool to jump in
+		 * without rmmod/insmod'ing.  show/store_requested_freq is also
+		 * darn handy for debugging
+		 */
+		if ( input > 100 )
+			input = 100;
+		dbs_tuners_ins.freq_step_percent = input;
+	}
+	up(&dbs_sem);
+	return count;
+}
+
+static ssize_t store_requested_freq(struct cpufreq_policy *policy,
+		const char *buf, size_t count)
+{
+	unsigned int input;
+	int ret;
+	ret = sscanf (buf, "%u", &input);
+	down(&dbs_sem);
+	if ( ret == 1 ) {
+		if ( input < policy->min )
+			input = policy->min;
+		if ( input > policy->max )
+			input = policy->max;
+		dbs_tuners_ins.requested_freq = input;
+		__cpufreq_driver_target(policy, input, CPUFREQ_RELATION_H);
+	}
+	up(&dbs_sem);
+	return count;
+}
+
 #define define_one_rw(_name) 					\
 static struct freq_attr _name = { 				\
 	.attr = { .name = __stringify(_name), .mode = 0644 }, 	\
@@ -200,6 +276,9 @@
 define_one_rw(sampling_down_factor);
 define_one_rw(up_threshold);
 define_one_rw(down_threshold);
+define_one_rw(requested_freq);
+define_one_rw(freq_step_percent);
+define_one_rw(ignore_nice);
 
 static struct attribute * dbs_attributes[] = {
 	&sampling_rate_max.attr,
@@ -208,6 +287,9 @@
 	&sampling_down_factor.attr,
 	&up_threshold.attr,
 	&down_threshold.attr,
+	&requested_freq.attr,
+	&freq_step_percent.attr,
+	&ignore_nice.attr,
 	NULL
 };
 
@@ -220,10 +302,9 @@
 
 static void dbs_check_cpu(int cpu)
 {
-	unsigned int idle_ticks, up_idle_ticks, down_idle_ticks;
-	unsigned int total_idle_ticks;
-	unsigned int freq_down_step;
-	unsigned int freq_down_sampling_rate;
+	unsigned int total_ticks, total_idle_ticks;
+	unsigned int ticks, idle_ticks;
+	unsigned int freq_step;
 	static int down_skip[NR_CPUS];
 	struct cpu_dbs_info_s *this_dbs_info;
 
@@ -242,26 +323,82 @@
 	 *
 	 * Any frequency increase takes it to the maximum frequency. 
 	 * Frequency reduction happens at minimum steps of 
-	 * 5% of max_frequency 
+	 * 5% (default) of max_frequency 
+	 *
+	 * My modified routine compares the number of idle ticks with the
+	 * expected number of idle ticks for the boundaries and acts accordingly
+	 * - Alexander Clouter <alex-kernel@digriz.org.uk>
 	 */
-	/* Check for frequency increase */
-	total_idle_ticks = kstat_cpu(cpu).cpustat.idle +
+
+	/* get various cpu stats */
+	total_ticks =
+		kstat_cpu(cpu).cpustat.user +
+		kstat_cpu(cpu).cpustat.nice +
+		kstat_cpu(cpu).cpustat.system +
+		kstat_cpu(cpu).cpustat.softirq +
+		kstat_cpu(cpu).cpustat.irq +
+		kstat_cpu(cpu).cpustat.idle +
+		kstat_cpu(cpu).cpustat.iowait;
+	total_idle_ticks =
+		kstat_cpu(cpu).cpustat.idle +
 		kstat_cpu(cpu).cpustat.iowait;
-	idle_ticks = total_idle_ticks -
-		this_dbs_info->prev_cpu_idle_up;
-	this_dbs_info->prev_cpu_idle_up = total_idle_ticks;
 
-	/* Scale idle ticks by 100 and compare with up and down ticks */
-	idle_ticks *= 100;
-	up_idle_ticks = (100 - dbs_tuners_ins.up_threshold) *
-			sampling_rate_in_HZ(dbs_tuners_ins.sampling_rate);
+	/* if the /sys says we need to consider nice tasks as 'idle' time too */
+	if (dbs_tuners_ins.ignore_nice == 0)
+		total_idle_ticks += kstat_cpu(cpu).cpustat.nice;
+	
+	ticks = (total_ticks -
+		this_dbs_info->prev_cpu_ticks) * 100;
+	idle_ticks = (total_idle_ticks -
+		this_dbs_info->prev_cpu_idle_ticks) * 100;
+	
+	this_dbs_info->prev_cpu_ticks = total_ticks;
+	this_dbs_info->prev_cpu_idle_ticks = total_idle_ticks;
+	
+	/* nothing to do if we cannot shift the frequency */
+	if (dbs_tuners_ins.freq_step_percent == 0)
+		return;
+	
+	/* checks to see if we have anything to do or can do and breaks out if:
+	 *  - we are within the 20% <-> 80% region
+	 *  - if the cpu freq needs increasing we are not already at max
+	 *  - if the cpu freq needs decreasing we are not already at min
+	 *
+	 *  you have to love those parentheses.... :)
+	 */
+	if (!( ( (ticks-idle_ticks) > (dbs_tuners_ins.up_threshold*idle_ticks)
+			&& dbs_tuners_ins.requested_freq
+				!= this_dbs_info->cur_policy->max
+	       )
+  	    || ( (ticks-idle_ticks) < (dbs_tuners_ins.down_threshold*idle_ticks)
+			&& dbs_tuners_ins.requested_freq
+				!= this_dbs_info->cur_policy->min
+	       ) ) )
+		return;
 
-	if (idle_ticks < up_idle_ticks) {
+	/* max freq cannot be less than 100. But who knows.... */
+	if (unlikely(this_dbs_info->cur_policy->max < 100)) {
+		freq_step = dbs_tuners_ins.freq_step_percent;
+	} else {
+		freq_step = (dbs_tuners_ins.freq_step_percent *
+				this_dbs_info->cur_policy->max) / 100;
+	}
+
+	/* Check for frequency increase */
+	if ( (ticks-idle_ticks) > (dbs_tuners_ins.up_threshold*idle_ticks) ) {
+		dbs_tuners_ins.requested_freq += freq_step;
+		if (dbs_tuners_ins.requested_freq >
+				this_dbs_info->cur_policy->max)
+			dbs_tuners_ins.requested_freq =
+				this_dbs_info->cur_policy->max;
+
+		/* printk("up: %u->%u\n",
+				this_dbs_info->cur_policy->cur,
+				dbs_tuners_ins.requested_freq); */
 		__cpufreq_driver_target(this_dbs_info->cur_policy,
-			this_dbs_info->cur_policy->max, 
-			CPUFREQ_RELATION_H);
+        	       	dbs_tuners_ins.requested_freq,
+        	       	CPUFREQ_RELATION_H);
 		down_skip[cpu] = 0;
-		this_dbs_info->prev_cpu_idle_down = total_idle_ticks;
 		return;
 	}
 
@@ -270,27 +407,19 @@
 	if (down_skip[cpu] < dbs_tuners_ins.sampling_down_factor)
 		return;
 
-	idle_ticks = total_idle_ticks -
-		this_dbs_info->prev_cpu_idle_down;
-	/* Scale idle ticks by 100 and compare with up and down ticks */
-	idle_ticks *= 100;
 	down_skip[cpu] = 0;
-	this_dbs_info->prev_cpu_idle_down = total_idle_ticks;
-
-	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 * this_dbs_info->cur_policy->max) / 100;
-
-		/* max freq cannot be less than 100. But who knows.... */
-		if (unlikely(freq_down_step == 0))
-			freq_down_step = 5;
-
+	if ( (ticks-idle_ticks) < (dbs_tuners_ins.down_threshold*idle_ticks) ) {
+		dbs_tuners_ins.requested_freq -= freq_step;
+		if (dbs_tuners_ins.requested_freq <
+				this_dbs_info->cur_policy->min)
+			dbs_tuners_ins.requested_freq =
+				this_dbs_info->cur_policy->min;
+		
+		/* printk("down: %u->%u\n",
+				this_dbs_info->cur_policy->cur,
+				dbs_tuners_ins.requested_freq); */
 		__cpufreq_driver_target(this_dbs_info->cur_policy,
-			this_dbs_info->cur_policy->cur - freq_down_step, 
+			dbs_tuners_ins.requested_freq, 
 			CPUFREQ_RELATION_H);
 		return;
 	}
@@ -344,10 +473,16 @@
 		down(&dbs_sem);
 		this_dbs_info->cur_policy = policy;
 		
-		this_dbs_info->prev_cpu_idle_up = 
+		this_dbs_info->prev_cpu_ticks =
+				kstat_cpu(cpu).cpustat.user +
+				kstat_cpu(cpu).cpustat.nice +
+				kstat_cpu(cpu).cpustat.system +
+				kstat_cpu(cpu).cpustat.softirq +
+				kstat_cpu(cpu).cpustat.irq +
 				kstat_cpu(cpu).cpustat.idle +
 				kstat_cpu(cpu).cpustat.iowait;
-		this_dbs_info->prev_cpu_idle_down = 
+		this_dbs_info->prev_cpu_idle_ticks = 
+				kstat_cpu(cpu).cpustat.nice +
 				kstat_cpu(cpu).cpustat.idle +
 				kstat_cpu(cpu).cpustat.iowait;
 		this_dbs_info->enable = 1;
@@ -368,7 +503,10 @@
 			def_sampling_rate = (latency / 1000) *
 					DEF_SAMPLING_RATE_LATENCY_MULTIPLIER;
 			dbs_tuners_ins.sampling_rate = def_sampling_rate;
-
+			dbs_tuners_ins.requested_freq
+				= this_dbs_info->cur_policy->cur;
+			dbs_tuners_ins.freq_step_percent = 5;
+			dbs_tuners_ins.ignore_nice = 0;
 			dbs_timer_init();
 		}
 		

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