From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751295AbcEJHH5 (ORCPT ); Tue, 10 May 2016 03:07:57 -0400 Received: from mga11.intel.com ([192.55.52.93]:56831 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751178AbcEJHH4 (ORCPT ); Tue, 10 May 2016 03:07:56 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,604,1455004800"; d="scan'208";a="802813316" Date: Tue, 10 May 2016 07:26:23 +0800 From: Yuyang Du To: Mike Galbraith Cc: Peter Zijlstra , Chris Mason , Ingo Molnar , Matt Fleming , linux-kernel@vger.kernel.org Subject: Re: sched: tweak select_idle_sibling to look for idle threads Message-ID: <20160509232623.GR16093@intel.com> References: <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> <1462786745.3803.181.camel@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1462786745.3803.181.camel@suse.de> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 09, 2016 at 11:39:05AM +0200, Mike Galbraith wrote: > 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. By cpu reservation, you mean the various averages in select_task_rq_fair? It does seem a lot of cleanup should be done. > > > > 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. I have to think this through, hot-potato. Maybe even droping it does not sound outrageous.