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Subject[PATCH] cpufreq: ondemand: Introduces stepped frequency increase
Date
The patch introduces a new sysfs tunable cpufreq/ondemand/freq_step,
as found in conservative governor, to chose the frequency increase step,
expressed as percentage (default = 100 is previous behaviour).

This allows fine tuning powersaving on mobile CPUs, since smaller steps will allow to:
* absorb punctual load spikes
* stabilize at the needed frequency, without passing for more power consuming states, and

Signed-off-by: Corrado Zoccolo czoccolo@gmail.com

---
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index e741c33..baa7b5e 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -83,6 +83,7 @@ struct cpu_dbs_info_s {
unsigned int freq_lo;
unsigned int freq_lo_jiffies;
unsigned int freq_hi_jiffies;
+ int requested_delta;
int cpu;
unsigned int enable:1,
sample_type:1;
@@ -112,11 +113,13 @@ static struct dbs_tuners {
unsigned int down_differential;
unsigned int ignore_nice;
unsigned int powersave_bias;
+ unsigned int freq_step;
} dbs_tuners_ins = {
.up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
.down_differential = DEF_FREQUENCY_DOWN_DIFFERENTIAL,
.ignore_nice = 0,
.powersave_bias = 0,
+ .freq_step = 100,
};

static inline cputime64_t get_cpu_idle_time_jiffy(unsigned int cpu,
@@ -261,6 +264,7 @@ show_one(sampling_rate, sampling_rate);
show_one(up_threshold, up_threshold);
show_one(ignore_nice_load, ignore_nice);
show_one(powersave_bias, powersave_bias);
+show_one(freq_step, freq_step);

static ssize_t store_sampling_rate(struct cpufreq_policy *unused,
const char *buf, size_t count)
@@ -358,6 +362,28 @@ static ssize_t store_powersave_bias(struct cpufreq_policy *unused,
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 :) */
+ mutex_lock(&dbs_mutex);
+ dbs_tuners_ins.freq_step = input;
+ mutex_unlock(&dbs_mutex);
+
+ return count;
+}
+
#define define_one_rw(_name) \
static struct freq_attr _name = \
__ATTR(_name, 0644, show_##_name, store_##_name)
@@ -366,6 +392,7 @@ define_one_rw(sampling_rate);
define_one_rw(up_threshold);
define_one_rw(ignore_nice_load);
define_one_rw(powersave_bias);
+define_one_rw(freq_step);

static struct attribute *dbs_attributes[] = {
&sampling_rate_max.attr,
@@ -374,6 +401,7 @@ static struct attribute *dbs_attributes[] = {
&up_threshold.attr,
&ignore_nice_load.attr,
&powersave_bias.attr,
+ &freq_step.attr,
NULL
};

@@ -464,19 +492,30 @@ static void dbs_check_cpu(struct cpu_dbs_info_s *this_dbs_info)

/* Check for frequency increase */
if (max_load_freq > dbs_tuners_ins.up_threshold * policy->cur) {
+ unsigned int freq_target = this_dbs_info->requested_delta
+ + policy->cur;
+ unsigned int freq_step;
+
/* if we are already at full speed then break out early */
- if (!dbs_tuners_ins.powersave_bias) {
- if (policy->cur == policy->max)
- return;
+ if (freq_target == policy->max)
+ return;
+
+ freq_step = (dbs_tuners_ins.freq_step * (policy->max-policy->min))
+ / 100;

- __cpufreq_driver_target(policy, policy->max,
- CPUFREQ_RELATION_H);
+ freq_target += max(freq_step, 5U);
+ freq_target = max(policy->min, min(policy->max, freq_target));
+
+ if (!dbs_tuners_ins.powersave_bias) {
+ __cpufreq_driver_target(policy, freq_target,
+ CPUFREQ_RELATION_H);
} else {
- int freq = powersave_bias_target(policy, policy->max,
- CPUFREQ_RELATION_H);
+ unsigned int freq = powersave_bias_target(policy, freq_target,
+ CPUFREQ_RELATION_H);
__cpufreq_driver_target(policy, freq,
CPUFREQ_RELATION_L);
}
+ this_dbs_info->requested_delta = freq_target - policy->cur;
return;
}

@@ -507,6 +546,7 @@ static void dbs_check_cpu(struct cpu_dbs_info_s *this_dbs_info)
__cpufreq_driver_target(policy, freq,
CPUFREQ_RELATION_L);
}
+ this_dbs_info->requested_delta = freq_next - policy->cur;
}
}



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