Hi Matthew, On Wed, Jul 8, 2009 at 6:10 PM, Matthew Garrett<mjg@xxxxxxxxxx> wrote: > On Wed, Jul 08, 2009 at 03:56:33PM +0200, Corrado Zoccolo wrote: >> The patch introduces a new sysfs tunable cpufreq/ondemand/freq_step, >> as found in conservative governor, to chose the frequency increase step, >> expressed as percentage (default = 100 is previous behaviour). >> >> This allows fine tuning powersaving on mobile CPUs, since smaller steps will allow to: >> * absorb punctual load spikes >> * stabilize at the needed frequency, without passing for more power consuming states, and > > Is this a measured powersaving? The ondemand model is based on the > assumption that the idle state is disproportionately lower in power than > any running state, and therefore it's more sensible to run flat out for > short periods of time than run at half speed for longer. Is this > inherently flawed, or is it an artifact of differences in your processor > design? The flawed assumption is that running at doubled frequency halves the completion time. On cpus that can change the core speed without impacting the memory-cache bandwidth (i.e. the Pentium M), workloads that access lot of memory go at the same speed at maximum and minimum frequency. Now I see new CPUs that can flush their cache during deep idle states (Atoms), this aggravates the aforementioned problem, rendering the high frequency state much less appetible. Corrado > > -- > Matthew Garrett | mjg59@xxxxxxxxxxxxx > -- __________________________________________________________________________ dott. Corrado Zoccolo mailto:czoccolo@xxxxxxxxx PhD - Department of Computer Science - University of Pisa, Italy -------------------------------------------------------------------------- -- 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
