Re: [PATCH] cpufreq: ondemand: Introduces stepped frequency increase

["Michael S. Zick" <lkml@morethan.org>]

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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