From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756661Ab3BVJ6O (ORCPT ); Fri, 22 Feb 2013 04:58:14 -0500 Received: from merlin.infradead.org ([205.233.59.134]:38742 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755501Ab3BVJ56 (ORCPT ); Fri, 22 Feb 2013 04:57:58 -0500 Message-ID: <1361527056.26780.55.camel@laptop> Subject: Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair() From: Peter Zijlstra To: Michael Wang Cc: Ingo Molnar , LKML , Paul Turner , Mike Galbraith , Andrew Morton , alex.shi@intel.com, Ram Pai , "Nikunj A. Dadhania" , Namhyung Kim Date: Fri, 22 Feb 2013 10:57:36 +0100 In-Reply-To: <51273636.6080907@linux.vnet.ibm.com> References: <51079178.3070002@linux.vnet.ibm.com> <20130220104958.GA9152@gmail.com> <5125A7C8.8020308@linux.vnet.ibm.com> <1361442055.26780.3.camel@laptop> <5126D9E0.7040108@linux.vnet.ibm.com> <1361522197.26780.39.camel@laptop> <51273636.6080907@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.2-0ubuntu0.1 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 Fri, 2013-02-22 at 17:11 +0800, Michael Wang wrote: > Ok, it do looks like wake_affine() lost it's value... I'm not sure we can say that on this one benchmark, there's a preemption advantage to running on a single cpu for pipe-test as well. We'd need to create a better benchmark to test this, one that has some actual data payload and control over the initial spread of the tasks or so. > > Now as far as I can see there's two options, either we find there's > > absolutely no benefit in wake_affine() as it stands today and we simply > > disable/remove it, or we go fix it. What we don't do is completely > > wreck it at atrocious cost. > > I get your point, we should replace wake_affine() with some feature > which could really achieve the goal to make client and server on same cpu. > > But is the logical that the waker/wakee are server/client(or reversed) > still works now? that sounds a little arbitrary to me... Ah, its never really been about server/client per-se. Its just a specific example -- one that breaks down with the 1:n pgbench situation. Wakeups in general can be considered to be a relation, suppose a hardware interrupt that received some data from a device and issues a wakeup to a task to consume this data. What CPU would be better suited to process this data then the one where its already cache hot.