On Tue, Apr 20, 2010 at 2:24 AM, Thomas Renninger <trenn@xxxxxxx> wrote: > On Monday 19 April 2010 15:43:25 Arjan van de Ven wrote: >> On Mon, 19 Apr 2010 10:29:47 +0200 >> Éric Piel <eric.piel@xxxxxxxxxxxxxxxx> wrote: >> > > >> > > The problem and fix are both verified with the "perf timechar" tool. >> > Hi, >> > I don't doubt that keeping the cpu full frequency during IO can >> > improve some specific workloads, however in your log message you >> > don't explain how much we are loosing. >> >> first of all, it's so bad that people will just turn the whole power >> management off... at which point fixing the really bad bug is actually >> quite a win > Not sure you fix a bug, I expect this was done on purpose. > The ondemand governor disadvantages processes with alternating short CPU > load peaks and idle sequences. > IO bound processes typically show up with such a behavior. > > But I follow Eric and agree that if it costs that much, changing > above sounds sane. > Still, I could imagine some people might want to not raise freq on IO bound > process activity, therefore this should get another ondemand param, similar > to ignore_nice_load. > I agree with Thomas here. Some of these assumptions on IO / FSB performance with cpu speed do not hold true on various ARM platforms. Perhaps we could have a min_io_freq value? Which is the min speed for the cpu to run at for IO bound activity. In the original patch, min_io_freq = scaling_max_freq. For various arm devices I can happily set min_io_freq to the lowest cpu speed that satisfies bus speeds. -- Mike > Thomas > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- 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
