linux-kernel - Re: [PATCH v3 2/3] PM / DEVFREQ: add example governors

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Date:	Mon, 4 Jul 2011 10:37:00 +0900
From:	MyungJoo Ham <myungjoo.ham@...sung.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Jiejing Zhang <kzjeef@...il.com>,
	Colin Cross <ccross@...gle.com>, Nishanth Menon <nm@...com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 2/3] PM / DEVFREQ: add example governors

Hello,

2011/7/3 Rafael J. Wysocki <rjw@...k.pl>:
> Hi,
>
> On Friday, May 27, 2011, MyungJoo Ham wrote:
>> Three CPUFREQ-like governors are provided as examples.
>>
>> powersave: use the lowest frequency possible. The user (device) should
>> set the polling_ms as 0 because polling is useless for this governor.
>>
>> performance: use the highest freqeuncy possible. The user (device)
>> should set the polling_ms as 0 because polling is useless for this
>> governor.
>>
>> simple_ondemand: simplified version of CPUFREQ's ONDEMAND governor.
>>
>> When a user updates OPP entries (enable/disable/add), OPP framework
>> automatically notifies DEVFREQ to update operating frequency
>> accordingly. Thus, DEVFREQ users (device drivers) do not need to update
>> DEVFREQ manually with OPP entry updates or set polling_ms for powersave
>> , performance, or any other "static" governors.
>>
>> Signed-off-by: MyungJoo Ham <myungjoo.ham@...sung.com>
>> Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
[]
>> +
>> +     /* Set the desired frequency based on the load */
>> +     a = (unsigned long long) stat.busy_time * stat.current_frequency;
>
> What's the purpose of the conversion?

Assuming that the work speed of a device is proportional to its
frequency, it measures the amount of work done.
It's time * work/time. For example, during the last 10 second, if the
busy_time was 5 sec and frequency was 10MHz,
it's "50M", which is same as 20MHz and 2.5 sec.

>
>> +     b = div_u64(a, stat.total_time);
>> +     b *= 100;
>> +     b = div_u64(b, (DFSO_UPTHRESHOLD - DFSO_DOWNDIFFERENCTIAL / 2));
>> +     *freq = (unsigned long) b;
>> +
>> +     return 0;
>> +}
>
> Rafael
>



-- 
MyungJoo Ham (함명주), Ph.D.
Mobile Software Platform Lab,
Digital Media and Communications (DMC) Business
Samsung Electronics
cell: 82-10-6714-2858
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