Hi Mike, On Fri, Aug 18, 2017 at 9:57 PM, Mike Galbraith <efa...@gmx.de> wrote: > On Fri, 2017-08-18 at 16:50 -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 high - as much 2% in my testing. On plotting >> signals, I found that there are errors especially high when we update just >> before the period boundary is hit. These errors can be significantly reduced >> if >> we update the averages more often. >> >> 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 512us). > > Ok, I gotta ask: In order to fix what? What exactly does the small > but existent overhead increase buy us other than an ever so slightly > different chart? What is your motivation to care about a microscopic > change in signal shape?
I wouldn't call the change "microscopic", its about 2% absolute which comes down to 1% with this change (if you count in relative terms, its higher and you can see the bump as the signal rises). If you look at the first chart at [1] at 3.74, that's not microscopic at all to me. Also about motivation, as I described in previous threads - I didn't nail this down to a particular change in behavior but other patches have been posted before that do things to improve signal accuracy, this is just one step in that direction. thanks, -Joel [1] https://github.com/joelagnel/joelagnel.github.io/blob/master/misc/pelt-error-v4.pdf > > -Mike > > -- > 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. >