linux-kernel - Re: [PATCH] cpufreq: governor: Be friendly towards latency-sensitive bursty workloads

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Date:	Tue, 03 Jun 2014 15:34:45 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	"ego@...ux.vnet.ibm.com" <ego@...ux.vnet.ibm.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: governor: Be friendly towards latency-sensitive
 bursty workloads

On 06/03/2014 03:09 PM, Viresh Kumar wrote:
> On 3 June 2014 15:02, Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
>> index e1c6433..3e8588f 100644
>> --- a/drivers/cpufreq/cpufreq_governor.c
>> +++ b/drivers/cpufreq/cpufreq_governor.c
>> @@ -36,14 +36,29 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu)
>>         struct od_dbs_tuners *od_tuners = dbs_data->tuners;
>>         struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
>>         struct cpufreq_policy *policy;
>> +       unsigned int sampling_rate;
>>         unsigned int max_load = 0;
>>         unsigned int ignore_nice;
>>         unsigned int j;
>>
>> -       if (dbs_data->cdata->governor == GOV_ONDEMAND)
>> +       if (dbs_data->cdata->governor == GOV_ONDEMAND) {
>> +               struct od_cpu_dbs_info_s *od_dbs_info;
>> +
>> +               /*
>> +                * Sometimes, the ondemand governor uses an additional
>> +                * multiplier to give long delays. So apply this multiplier to
>> +                * the 'sampling_rate', so as to keep the wake-up-from-idle
>> +                * detection logic a bit conservative.
>> +                */
>> +               sampling_rate = od_tuners->sampling_rate;
>> +               od_dbs_info = dbs_data->cdata->get_cpu_dbs_info_s(cpu);
> 
> Probably do both above right after definition of od_dbs_info or merge
> above with it. and just keep below after the comment ?
> 
>> +               sampling_rate *= od_dbs_info->rate_mult;
> 

Well, the method I used keeps the organization such that the code following
the comment does precisely what the comment says (i.e, get the sampling_rate,
fetch the multiplier, and then multiply). So I feel it makes it easier to
understand.

Regards,
Srivatsa S. Bhat

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