From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752530AbcEIJjK (ORCPT ); Mon, 9 May 2016 05:39:10 -0400 Received: from mx2.suse.de ([195.135.220.15]:51928 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751400AbcEIJjI (ORCPT ); Mon, 9 May 2016 05:39:08 -0400 Message-ID: <1462786745.3803.181.camel@suse.de> Subject: Re: sched: tweak select_idle_sibling to look for idle threads From: Mike Galbraith To: Yuyang Du Cc: Peter Zijlstra , Chris Mason , Ingo Molnar , Matt Fleming , linux-kernel@vger.kernel.org Date: Mon, 09 May 2016 11:39:05 +0200 In-Reply-To: <20160509011311.GQ16093@intel.com> References: <20160430124731.GE2975@worktop.cust.blueprintrf.com> <1462086753.9717.29.camel@suse.de> <20160501085303.GF2975@worktop.cust.blueprintrf.com> <1462094425.9717.45.camel@suse.de> <20160507012417.GK16093@intel.com> <1462694935.4155.83.camel@suse.de> <20160508185747.GL16093@intel.com> <1462765540.3803.44.camel@suse.de> <20160508202201.GM16093@intel.com> <1462779853.3803.128.camel@suse.de> <20160509011311.GQ16093@intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2016-05-09 at 09:13 +0800, Yuyang Du wrote: > On Mon, May 09, 2016 at 09:44:13AM +0200, Mike Galbraith wrote: > > In a perfect world, running only Chris' benchmark on an otherwise idle > > box, there would never _be_ any work to steal. > > What is the perfect world like? I don't get what you mean. In a perfect world from this benchmark's perspective, when you fork or wake while box is underutilized, wakee/child lands on an idle CPU. To this benchmark, anything else is broken. > > In the real world, we > > smooth utilization, optimistically peek at this/that, and intentionally > > throttle idle balancing (etc etc), which adds up to an imperfect world > > for this (based on real world load) benchmark. > > So, is this a shout-out: these parts should be coordinated better? Switching to instantaneous load along with the cpu reservation hackery made Chris's benchmark a happy camper. Is that the answer? Nope, just verification of the where the problem lives. > > > En... should we try remove recording last_wakee? > > > > The more the merrier, go for it! :) > > Nuh, really, this heuristic is too heuristic, :) > The totality of all possible cases is scary. Well, make it better. The author provided evidence when it was born. -Mike