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References: <200907081556.34682.czoccolo@gmail.com>
	 <200907080918.41167.lkml@morethan.org>
Date: Wed, 8 Jul 2009 19:45:43 +0200
Message-ID: <4e5e476b0907081045g60ceed3cm6e1277c631169f18@mail.gmail.com>
Subject: Re: [PATCH] cpufreq: ondemand: Introduces stepped frequency increase
From: Corrado Zoccolo <czoccolo@gmail.com>
To: lkml@morethan.org
Cc: Dave Jones <davej@redhat.com>, linux-kernel@vger.kernel.org,
       cpufreq@vger.kernel.org
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Hi Michael,
On Wed, Jul 8, 2009 at 4:18 PM, Michael S. Zick<lkml@morethan.org> wrote:
> 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.
>
Using the correct clock multipliers and voltages is driver's duty.
This change affects the governor, instead, that selects, among the
available ones,
which one will be used, according to a policy.

Corrado

> 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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>>
>
>
>


-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@gmail.com
PhD - Department of Computer Science - University of Pisa, Italy
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