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
