linux-kernel - Re: [RFC PATCH 3/4] cpufreq: Add Active Stats calls tracking frequency changes

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Date:   Tue, 22 Jun 2021 12:07:14 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org,
        linux-pm@...r.kernel.org, amitk@...nel.org, rui.zhang@...el.com,
        dietmar.eggemann@....com, Chris.Redpath@....com,
        Beata.Michalska@....com, rjw@...ysocki.net, amit.kachhap@...il.com
Subject: Re: [RFC PATCH 3/4] cpufreq: Add Active Stats calls tracking
 frequency changes



On 6/22/21 10:32 AM, Viresh Kumar wrote:
> Not commenting on the idea itself but just the code changes here.
> 
> On 22-06-21, 08:59, Lukasz Luba wrote:
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index 802abc925b2a..d79cb9310572 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -14,6 +14,7 @@
>>   
>>   #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>>   
>> +#include <linux/active_stats.h>
>>   #include <linux/cpu.h>
>>   #include <linux/cpufreq.h>
>>   #include <linux/cpu_cooling.h>
>> @@ -387,6 +388,8 @@ static void cpufreq_notify_transition(struct cpufreq_policy *policy,
>>   
>>   		cpufreq_stats_record_transition(policy, freqs->new);
>>   		policy->cur = freqs->new;
>> +
>> +		active_stats_cpu_freq_change(policy->cpu, freqs->new);
>>   	}
>>   }
>>   
>> @@ -2085,6 +2088,8 @@ unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
>>   			    policy->cpuinfo.max_freq);
>>   	cpufreq_stats_record_transition(policy, freq);
>>   
>> +	active_stats_cpu_freq_fast_change(policy->cpu, freq);
>> +
> 
> It would have been better if you would have modified
> cpufreq_stats_record_transition() instead, since that is there for
> similar kind of stats.

That cpufreq_stats_record_transition() is present only if
CONFIG_CPU_FREQ_STAT is set. I didn't wanted to be dependent on
this config.

> 
> Plus don't you need to record this for all policy->cpus instead of
> just policy->cpu ?
> 

It will be accounted for all cpus in that freq domain. The
active_stats_cpu_freq_fast_change() implementation uses
a shared structure (single for whole domain) 'shared_ast':
_active_stats_cpu_freq_change(ast->shared_ast, freq, ts)
(from patch 1/4)