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

[MyungJoo Ham]

Hello,

2011/7/3 Rafael J. Wysocki <rjw@xxxxxxx>:
> 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@xxxxxxxxxxx>
>> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
[]
>> +
>> + Â Â /* Set the desired frequency based on the load */
>> + Â Â 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.

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



-- 
MyungJoo Ham (íëì), Ph.D.
Mobile Software Platform Lab,
Digital Media and Communications (DMC) Business
Samsung Electronics
cell: 82-10-6714-2858
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/