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    SubjectRe: [PATCH] cpufreq: ondemand: Introduces stepped frequency increase
    Date
    On Wed July 8 2009, Corrado Zoccolo wrote:
    > 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
    >

    Has this been tested on VIA C7-M and similar VIA products?
    Reason I ask is because they only step in increments of the
    clock multiplier - which varies among the models.

    Also, the factory recommendation is to stay on the freq/voltage
    curve for each product.
    Only the programmer accessable VID (Voltage IDentifier) codes
    are (on-silicon) lookup table mapped to the VRM (Voltage Regulator Module)
    control lines - not all products provide an "on curve" mapping
    for each possible multiplier step.

    How about a few conditional statements in this bit of code, please.

    Mike
    > 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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