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? > 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?
