[patch 6/6] cpufreq: Add idle microaccounting in ondemand governor

[venkatesh.pallipadi@intel.com]

[-- Attachment #1: intro_idle_microaccounting.patch --]
[-- Type: text/plain, Size: 3542 bytes --]

Use get_cpu_idle_time_us() to get micro-accounted idle information.
This enables ondemand to get more accurate idle and busy timings
than the jiffy based calculation. As a result, we can decrease
the ondemand safety gaurd band from 80-10 to 95-3.

Results in more aggressive power savings.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>

---
 drivers/cpufreq/cpufreq_ondemand.c |   46 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

Index: linux-2.6/drivers/cpufreq/cpufreq_ondemand.c
===================================================================
--- linux-2.6.orig/drivers/cpufreq/cpufreq_ondemand.c	2008-07-17 13:19:08.000000000 -0700
+++ linux-2.6/drivers/cpufreq/cpufreq_ondemand.c	2008-07-17 13:27:33.000000000 -0700
@@ -18,6 +18,9 @@
 #include <linux/jiffies.h>
 #include <linux/kernel_stat.h>
 #include <linux/mutex.h>
+#include <linux/hrtimer.h>
+#include <linux/tick.h>
+#include <linux/ktime.h>
 
 /*
  * dbs is used in this file as a shortform for demandbased switching
@@ -26,6 +29,8 @@
 
 #define DEF_FREQUENCY_DOWN_DIFFERENTIAL		(10)
 #define DEF_FREQUENCY_UP_THRESHOLD		(80)
+#define MICRO_FREQUENCY_DOWN_DIFFERENTIAL	(3)
+#define MICRO_FREQUENCY_UP_THRESHOLD		(95)
 #define MIN_FREQUENCY_UP_THRESHOLD		(11)
 #define MAX_FREQUENCY_UP_THRESHOLD		(100)
 
@@ -58,6 +63,7 @@ enum {DBS_NORMAL_SAMPLE, DBS_SUB_SAMPLE}
 struct cpu_dbs_info_s {
 	cputime64_t prev_cpu_idle;
 	cputime64_t prev_cpu_wall;
+	cputime64_t prev_cpu_nice;
 	struct cpufreq_policy *cur_policy;
  	struct delayed_work work;
 	struct cpufreq_frequency_table *freq_table;
@@ -97,7 +103,8 @@ static struct dbs_tuners {
 	.powersave_bias = 0,
 };
 
-static inline cputime64_t get_cpu_idle_time(unsigned int cpu, cputime64_t *wall)
+static inline cputime64_t get_cpu_idle_time_jiffy(unsigned int cpu,
+							cputime64_t *wall)
 {
 	cputime64_t idle_time;
 	cputime64_t cur_wall_time;
@@ -123,6 +130,33 @@ static inline cputime64_t get_cpu_idle_t
 	return idle_time;
 }
 
+static inline cputime64_t get_cpu_idle_time(unsigned int cpu, cputime64_t *wall)
+{
+	u64 idle_time = get_cpu_idle_time_us(cpu, wall);
+
+	if (idle_time == -1ULL)
+		return get_cpu_idle_time_jiffy(cpu, wall);
+
+	if (dbs_tuners_ins.ignore_nice) {
+		cputime64_t cur_nice;
+		unsigned long cur_nice_jiffies;
+		struct cpu_dbs_info_s *dbs_info;
+
+		dbs_info = &per_cpu(cpu_dbs_info, cpu);
+		cur_nice = cputime64_sub(kstat_cpu(cpu).cpustat.nice,
+					 dbs_info->prev_cpu_nice);
+		/*
+		 * Assumption: nice time between sampling periods will be
+		 * less than 2^32 jiffies for 32 bit sys
+		 */
+		cur_nice_jiffies = (unsigned long)
+					cputime64_to_jiffies64(cur_nice);
+		dbs_info->prev_cpu_nice = kstat_cpu(cpu).cpustat.nice;
+		return idle_time + jiffies_to_usecs(cur_nice_jiffies);
+	}
+	return idle_time;
+}
+
 /*
  * Find right freq to be set now with powersave_bias on.
  * Returns the freq_hi to be used right now and will set freq_hi_jiffies,
@@ -602,6 +636,16 @@ EXPORT_SYMBOL(cpufreq_gov_ondemand);
 
 static int __init cpufreq_gov_dbs_init(void)
 {
+	cputime64_t wall;
+	u64 idle_time = get_cpu_idle_time_us(smp_processor_id(), &wall);
+
+	if (idle_time != -1ULL) {
+		/* Idle micro accounting is supported. Use finer thresholds */
+		dbs_tuners_ins.up_threshold = MICRO_FREQUENCY_UP_THRESHOLD;
+		dbs_tuners_ins.down_differential =
+					MICRO_FREQUENCY_DOWN_DIFFERENTIAL;
+	}
+
 	kondemand_wq = create_workqueue("kondemand");
 	if (!kondemand_wq) {
 		printk(KERN_ERR "Creation of kondemand failed\n");

--