On 14 April 2017 at 10:49, Vincent Guittot <[email protected]> wrote: > On 13 April 2017 at 18:13, Peter Zijlstra <[email protected]> wrote: >> 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. > > yes make sense > >> >> 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. > > I'm going to make it a try to check that it removes the variation i'm seeing
I have sent a patchset based on your proposal that fix this variation issue > >> >> (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).
