On Mon, Jul 4, 2011 at 5:43 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > On Monday, July 04, 2011, MyungJoo Ham wrote: >> 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> >> [] >> >> + >> >> + /* 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. > > I understand that, but my question was why you're doing a forced conversion > to (unsigned long long). Ah.. that was for the 64bit operations. Both busy_time and current_frequency are 32bit and current_frequency may be a big number. Thus, in order to get "freq" value without losing bits (e.g., if current_frequency = 1GHz and busy_time = 8000, we get an overflow without 64bit operations), I've inserted 64bit operations with the conversion. For the cosmetic reasons, it appears that "u64" looks better though. > > Thanks, > Rafael > Thank you. - MyungJoo -- MyungJoo Ham, Ph.D. Mobile Software Platform Lab, Digital Media and Communications (DMC) Business Samsung Electronics cell: 82-10-6714-2858 _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
