Thanks David. If I would like to fine tune up_threshold and sampling_down_factor for say OMAP platform, is there any way to do it in kernel itself? I know these are configurable via sysfs entries. But if I want to optimize them in kernel itself, is there anyway? I see that default values are set in cpufreq-ondemand.c which is common kernel file. I would like to know if these can be set in platform specific code? Vishwa On Wed, Nov 24, 2010 at 7:42 PM, David C Niemi <dniemi@xxxxxxxxxxxx> wrote: > > Thanks for running the tests, Vishwa. Your results are what I'd expect > but it's good to see independent confirmation. In my benchmarks I saw > 95-100% of the performance governor's performance, but the conditions > were more favorable and the original ondemand governor was "only" > degrading performance 20-30% to begin with. > > There should be absolutely no changes in power consumption at all for > the patch itself, as behavior does not change until you raise > sampling_down_factor above 1 (the default). If you set it high, I would > expect higher power consumption (but also higher performance) under load > and no change in power consumption when idle or close to idle. Setting > a high sampling_down_factor causes the governor to reevaluate load less > often when at max cpu speed, both to reduce overhead and to let it > remain at maximum performance more consistently. Without this change, > the ondemand governor jitters a lot in and out of max clock speed when > under high loads, which is why its performance can be much worse than > the performance governor. Reducing the number of transitions and load > evaluations should also improve performance per watt, though the details > of that depend on the relative efficiency of the CPU's respective clock > speeds. > > If you want to balance power consumption and performance, a middle > setting of sampling_down_factor like "10" should make a noticeable > improvement in performance while not having as much impact on power. > But if you want to match the performance governor's performance and are > less concerned about transient power consumption, you will want to set > it higher. > > Another note: I recommend setting io_is_busy to 1 when using > sampling_down_factor above 1, as it improves responsiveness to quick > load transients involving some I/O. It's also worth considering > lowering up_threshold to 50 or even down to 15-20. > > David C Niemi > > Vishwanath Sripathy wrote: >> Amit, >> >> On Tue, Nov 23, 2010 at 8:22 PM, Amit Kucheria <amit.kucheria@xxxxxxxxxx> wrote: >> >>> Vishwa, >>> >>> Have you had a chance to do some usetime tests with these changes? >>> >> I did test USB performance with this and I see ondmeand is 90% close >> to performance. >> >>> It would be interesting to measure the power consumption with and >>> without these changes. >>> >> Power consumption impact can vary from usecase to usecase and extra >> performance will have some power impact. >> However in idle scenario, I feel this should not have much impact >> since ondemand timer is a deferrable timer which means that it does >> not prevent cpuidle. I will try to measure it for some usecase and >> compare the power impact. >> >> Vishwa >> > -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
