Hi Peter, On Mon, Aug 7, 2017 at 6:40 AM, Peter Zijlstra <pet...@infradead.org> wrote: > On Fri, Aug 04, 2017 at 08:40:23AM -0700, Joel Fernandes wrote: >> The PELT signal (sa->load_avg and sa->util_avg) are not updated if the >> amount accumulated during a single update doesn't cross a period >> boundary. > >> This is fine in cases where the amount accrued is much smaller than >> the size of a single PELT window (1ms) however if the amount accrued >> is high then the relative error (calculated against what the actual >> signal would be had we updated the averages) can be quite high - as >> much 3-6% in my testing. > > The max accumulate we can have and not cross a boundary is 1023*1024 ns. > At which point we get a divisor of LOAD_AVG_MAX - 1024 + 1023. > > So for util_sum we'd have a increase of 1023*1024/(47742-1) = ~22. Which > on the total signal for util (1024) is ~2.1% > > Where does the 3-6% come from?
Sorry, I should have been more clear. This error (3-6%) I measured is relative to what the signal could have been had we done the division. Indeed I don't see any cases were the absolute error is more than ~22 / 1024 as you mentioned. > >> Inorder to fix this, this patch does the average update by also >> checking how much time has elapsed since the last update and update >> the averages if it has been long enough (as a threshold I chose >> 128us). > > This of course does the divisions more often; anything on performance > impact? Sure, I am working on those and will post an update soon. Thanks! -Joel > > -- > You received this message because you are subscribed to the Google Groups > "kernel-team" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to kernel-team+unsubscr...@android.com. >