linux-kernel - Re: [PATCH V5 1/2] cpufreq: Handle sorted frequency tables more efficiently

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Date:	Mon, 27 Jun 2016 12:10:52 +0200
From:	Francesco Lavra <francescolavra.fl@...il.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Rafael Wysocki <rjw@...ysocki.net>
Cc:	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH V5 1/2] cpufreq: Handle sorted frequency tables more
 efficiently

Hi,

On 06/27/2016 06:29 AM, Viresh Kumar wrote:
> cpufreq drivers aren't required to provide a sorted frequency table
> today, and even the ones which provide a sorted table aren't handled
> efficiently by cpufreq core.
>
> This patch adds infrastructure to verify if the freq-table provided by
> the drivers is sorted or not, and use efficient helpers if they are
> sorted.
<snip>
> @@ -610,6 +617,227 @@ int cpufreq_boost_trigger_state(int state);
>   int cpufreq_boost_enabled(void);
>   int cpufreq_enable_boost_support(void);
>   bool policy_has_boost_freq(struct cpufreq_policy *policy);
> +
> +/* Find lowest freq at or above target in a table in ascending order */
> +static inline int cpufreq_table_find_index_al(struct cpufreq_policy *policy,
> +					      unsigned int target_freq)
> +{
> +	struct cpufreq_frequency_table *table = policy->freq_table;
> +	unsigned int freq;
> +	int i, best = -1;
> +
> +	for (i = 0; table[i].frequency != CPUFREQ_TABLE_END; i++) {
> +		freq = table[i].frequency;
> +
> +		if (freq >= target_freq)
> +			return i;
> +
> +		best = i;
> +	}
> +
> +	return best;
> +}
> +
> +/* Find lowest freq at or above target in a table in descending order */
> +static inline int cpufreq_table_find_index_dl(struct cpufreq_policy *policy,
> +					      unsigned int target_freq)
> +{
> +	struct cpufreq_frequency_table *table = policy->freq_table;
> +	unsigned int freq;
> +	int i, best = -1;
> +
> +	for (i = 0; table[i].frequency != CPUFREQ_TABLE_END; i++) {
> +		freq = table[i].frequency;
> +
> +		if (freq == target_freq)
> +			return i;
> +
> +		if (freq > target_freq) {
> +			best = i;
> +			continue;
> +		}
> +
> +		/* No freq found below target_freq */

"below" should be "above"

> +/* Find closest freq to target in a table in ascending order */
> +static inline int cpufreq_table_find_index_ac(struct cpufreq_policy *policy,
> +					      unsigned int target_freq)
> +{
> +	struct cpufreq_frequency_table *table = policy->freq_table;
> +	unsigned int freq;
> +	int i, best = -1;
> +
> +	for (i = 0; table[i].frequency != CPUFREQ_TABLE_END; i++) {
> +		freq = table[i].frequency;
> +
> +		if (freq == target_freq)
> +			return i;
> +
> +		if (freq < target_freq) {
> +			best = i;
> +			continue;
> +		}
> +
> +		/* No freq found below target_freq */
> +		if (best == -1)
> +			return i;
> +
> +		/* Choose the closest freq */
> +		if (target_freq - table[best].frequency > freq - target_freq)
> +			return i;
> +
> +		return best;
> +	}
> +
> +	return best;
> +}
> +
> +/* Find closest freq to target in a table in descending order */
> +static inline int cpufreq_table_find_index_dc(struct cpufreq_policy *policy,
> +					      unsigned int target_freq)
> +{
> +	struct cpufreq_frequency_table *table = policy->freq_table;
> +	unsigned int freq;
> +	int i, best = -1;
> +
> +	for (i = 0; table[i].frequency != CPUFREQ_TABLE_END; i++) {
> +		freq = table[i].frequency;
> +
> +		if (freq == target_freq)
> +			return i;
> +
> +		if (freq > target_freq) {
> +			best = i;
> +			continue;
> +		}
> +
> +		/* No freq found below target_freq */

"below" should be "above"

> +		if (best == -1)
> +			return i;
> +
> +		/* Choose the closest freq */
> +		if (target_freq - table[best].frequency > freq - target_freq)

Here, table[best].frequency > target_freq, and freq < and target_freq, 
so you should reverse the sign of both sides of the inequation:

	if (table[best].frequency - target_freq > target_freq - freq)

> +			return i;
> +
> +		return best;
> +	}
> +
> +	return best;
> +}

Regards,
Francesco