On Monday, July 04, 2011, MyungJoo Ham wrote: > 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. You wouldn't need the explicit type casting if you did a = stat.busy_time; a *= stat.current_frequency; Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
