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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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