On Thu, Apr 13, 2017 at 05:16:20PM +0200, Vincent Guittot wrote: > On 13 April 2017 at 15:39, Peter Zijlstra <[email protected]> wrote:
> > OK, so the reason util_avg varies is because we compute it wrong. And I > > think we can easily fix that once we pull out all the factors (which > > would mean your patch and the pulling out of weight patch which still > > needs to be finished). > > That would be great to remove this unwanted variation. So the problem with the _avg stuff is that we include the d3 segment, that is the unfinished current window. Since we only re-compute the _avg whenever we roll over, the intent already seems to be to only compute it on completed windows. But because 'complicated/expensive', its hard to not include d3 and thus we get the wobble. Once we compute pure running/runnable sums, without extra contrib factors, we can simply subtract our d3 term from sum when doing the division and change the divider to LOAD_AVG_MAX*y, getting the stable _avg over all completed windows. (you could do the same with factors, but then we get to do a bunch of extra multiplications which aren't free). > > > > But you're comparing against util_sum here, that behaves slightly > > different. I think you want 'util_sum >= 1024 * (LOAD_AVG_MAX - 1024)' > > instead. > > yes, the variation happens on the util_sum Well, for util_sum its simple to ignore the current window, which is what the suggested equation does (note that LOAD_AVG_MAX*y == LOAD_AVG_MAX-1024).
