From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S642206AbdD1RqY (ORCPT ); Fri, 28 Apr 2017 13:46:24 -0400 Received: from mail-yw0-f195.google.com ([209.85.161.195]:35081 "EHLO mail-yw0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2999309AbdD1RqR (ORCPT ); Fri, 28 Apr 2017 13:46:17 -0400 Date: Fri, 28 Apr 2017 13:46:15 -0400 From: Tejun Heo To: Vincent Guittot Cc: Ingo Molnar , Peter Zijlstra , linux-kernel , Linus Torvalds , Mike Galbraith , Paul Turner , Chris Mason , kernel-team@fb.com Subject: Re: [PATCH 1/2] sched/fair: Fix how load gets propagated from cfs_rq to its sched_entity Message-ID: <20170428174615.GB4628@htj.duckdns.org> References: <20170424201344.GA14169@wtj.duckdns.org> <20170424201415.GB14169@wtj.duckdns.org> <20170426222744.GA9616@wtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.8.0 (2017-02-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Vincent. On Thu, Apr 27, 2017 at 10:59:12AM +0200, Vincent Guittot wrote: > > But the only difference there is that we lose accuracy in calculation; > > otherwise, the end results are the same, no? > > Yes the end result is the same, it was mainly to point out the range > difference and explain why we need scale_load_down(shares) for the 2nd > argument of min. > This should also explain the warning issue you mentioned earlier I'm not sure this makes sense. Practically, we're doing more shifts just to lose calculation accuracy. Even conceptually, what we're doing is C A * --- B Where A is in a different scale while B and C are in the same. What you're suggesting is scale_down(C) A * --------------- scale_down(B) I can't see why this is better in any way. Thanks. -- tejun