Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964991AbdCVRDj (ORCPT ); Wed, 22 Mar 2017 13:03:39 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:41024 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935561AbdCVRCL (ORCPT ); Wed, 22 Mar 2017 13:02:11 -0400 Date: Wed, 22 Mar 2017 18:02:04 +0100 From: Peter Zijlstra To: Joel Fernandes Cc: LKML , Paul Turner , Dietmar Eggemann , Juri Lelli , Patrick Bellasi , Ingo Molnar Subject: Re: [PATCH] sched: fair: Improve PELT decay_load calculation comments Message-ID: <20170322170204.hacokajtuabrjlia@hirez.programming.kicks-ass.net> References: <20170310202341.11449-1-joelaf@google.com> <20170322141626.isj3dlrimppwq2xv@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1318 Lines: 31 On Wed, Mar 22, 2017 at 09:35:43AM -0700, Joel Fernandes wrote: > On Wed, Mar 22, 2017 at 7:16 AM, Peter Zijlstra wrote: > > On Fri, Mar 10, 2017 at 12:23:41PM -0800, Joel Fernandes wrote: > >> The PELT decay_load comments are a bit confusing, first of all > >> the 1/2^N should be (1/2)^N so that the reader doesn't get confused. > > > > I'm thinking you're confused. They're identical. > > > > (1/2)^N = (2^-1)^N = 2^-N = 1/2^N > > They are identical I know, but I meant by enclosing the 1/2 in > brackets, it is more clear that we multiply by 1/2 N times to the > first time reader - for the reason that we'd like to reduce the PELT > calculated load by 1/2 N times. Must be me then, because I've never been confused about that. Esp. so since the first part: y^p = 1/2, explicitly mentions half. So its clear from the factorization that half is meant. > >> Secondly, the y^N splitting into a 2-part decay factor deserves > >> a better explanation. This patch improves the comments. > > > > I find its actually harder to read. > > Oh, which part? Can you help improve it? Maybe I didn't word something > correctly? I think the fact that there's now words actually makes it worse. The equation very concisely shows what we do. I don't see why we need extra words there to obscure things.