[CPUFREQ] ondemand governor automatic downscaling

[PATCH] [4/5] ondemand governor automatic downscaling

Here is a change of policy for the ondemand governor. The modification
concerns the frequency downscaling. Instead of decreasing to a lower
frequency when the CPU usage is under 20%, this new policy automatically
scales to the optimal frequency. The optimal frequency being the lowest
frequency which provides enough power to not trigger the upscaling policy.

Signed-off-by: Eric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Dave Jones <davej@redhat.com>

1 files changed, 25 insertions, 92 deletions

diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 0482bd49aba8..8bc38ab96400 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -34,13 +34,9 @@
  */
 
 #define DEF_FREQUENCY_UP_THRESHOLD              (80)
-#define MIN_FREQUENCY_UP_THRESHOLD              (0)
+#define MIN_FREQUENCY_UP_THRESHOLD              (11)
 #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
@@ -77,14 +73,11 @@ struct dbs_tuners {
         unsigned int            sampling_rate;
         unsigned int            sampling_down_factor;
         unsigned int            up_threshold;
-        unsigned int            down_threshold;
         unsigned int            ignore_nice;
-        unsigned int            freq_step;
 };
 
 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,
 };
 
@@ -125,9 +118,7 @@ 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);
 show_one(ignore_nice, ignore_nice);
-show_one(freq_step, freq_step);
 
 static ssize_t store_sampling_down_factor(struct cpufreq_policy *unused, 
                 const char *buf, size_t count)
@@ -173,8 +164,7 @@ static ssize_t store_up_threshold(struct cpufreq_policy *unused,
 
         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;
         }
@@ -185,27 +175,6 @@ static ssize_t store_up_threshold(struct cpufreq_policy *unused,
         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;
-}
-
 static ssize_t store_ignore_nice(struct cpufreq_policy *policy,
                 const char *buf, size_t count)
 {
@@ -240,29 +209,6 @@ static ssize_t store_ignore_nice(struct cpufreq_policy *policy,
         return count;
 }
 
-static ssize_t store_freq_step(struct cpufreq_policy *policy,
-                const char *buf, size_t count)
-{
-        unsigned int input;
-        int ret;
-
-        ret = sscanf (buf, "%u", &input);
-
-        if ( ret != 1 )
-                return -EINVAL;
-
-        if ( input > 100 )
-                input = 100;
-        
-        /* no need to test here if freq_step is zero as the user might actually
-         * want this, they would be crazy though :) */
-        down(&dbs_sem);
-        dbs_tuners_ins.freq_step = input;
-        up(&dbs_sem);
-
-        return count;
-}
-
 #define define_one_rw(_name) \
 static struct freq_attr _name = \
 __ATTR(_name, 0644, show_##_name, store_##_name)
@@ -270,9 +216,7 @@ __ATTR(_name, 0644, show_##_name, store_##_name)
 define_one_rw(sampling_rate);
 define_one_rw(sampling_down_factor);
 define_one_rw(up_threshold);
-define_one_rw(down_threshold);
 define_one_rw(ignore_nice);
-define_one_rw(freq_step);
 
 static struct attribute * dbs_attributes[] = {
         &sampling_rate_max.attr,
@@ -280,9 +224,7 @@ static struct attribute * dbs_attributes[] = {
         &sampling_rate.attr,
         &sampling_down_factor.attr,
         &up_threshold.attr,
-        &down_threshold.attr,
         &ignore_nice.attr,
-        &freq_step.attr,
         NULL
 };
 
@@ -295,8 +237,8 @@ static struct attribute_group dbs_attr_group = {
 
 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;
@@ -310,17 +252,15 @@ static void dbs_check_cpu(int cpu)
 
         policy = this_dbs_info->cur_policy;
         /* 
-         * The default safe range is 20% to 80% 
-         * Every sampling_rate, we check
-         *      - If current idle time is less than 20%, then we try to 
-         *        increase frequency
-         * Every sampling_rate*sampling_down_factor, we check
-         *      - If current idle time is more than 80%, then we try to
-         *        decrease frequency
+         * Every sampling_rate, we check, if current idle time is less
+         * than 20% (default), then we try to increase frequency
+         * Every sampling_rate*sampling_down_factor, we look for a the lowest
+         * frequency which can sustain the load while keeping idle time over
+         * 30%. If such a frequency exist, we try to decrease to this frequency.
          *
          * Any frequency increase takes it to the maximum frequency. 
          * Frequency reduction happens at minimum steps of 
-         * 5% (default) of max_frequency 
+         * 5% (default) of current frequency 
          */
 
         /* Check for frequency increase */
@@ -383,33 +323,27 @@ 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;
+        /* if we cannot reduce the frequency anymore, break out early */
+        if (policy->cur == policy->min)
+                return;
 
+        /* 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) *
-                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
-                 * or if we 'cannot' reduce the speed as the user might want
-                 * freq_step to be zero */
-                if (policy->cur == policy->min || dbs_tuners_ins.freq_step == 0)
-                        return;
+        total_ticks = usecs_to_jiffies(freq_down_sampling_rate);
 
-                freq_down_step = (dbs_tuners_ins.freq_step * policy->max) / 100;
-
-                /* max freq cannot be less than 100. But who knows.... */
-                if (unlikely(freq_down_step == 0))
-                        freq_down_step = 5;
+        /*
+         * 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) / total_ticks;
+        freq_next = (freq_next * policy->cur) / 
+                        (dbs_tuners_ins.up_threshold - 10);
 
-                __cpufreq_driver_target(policy,
-                        policy->cur - freq_down_step,
-                        CPUFREQ_RELATION_H);
-                return;
-        }
+        if (freq_next <= ((policy->cur * 95) / 100))
+                __cpufreq_driver_target(policy, freq_next, CPUFREQ_RELATION_L);
 }
 
 static void do_dbs_timer(void *data)
@@ -487,7 +421,6 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                                         DEF_SAMPLING_RATE_LATENCY_MULTIPLIER;
                         dbs_tuners_ins.sampling_rate = def_sampling_rate;
                         dbs_tuners_ins.ignore_nice = 0;
-                        dbs_tuners_ins.freq_step = 5;
 
                         dbs_timer_init();
                 }