From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932444Ab2AJQun (ORCPT ); Tue, 10 Jan 2012 11:50:43 -0500 Received: from e23smtp08.au.ibm.com ([202.81.31.141]:38309 "EHLO e23smtp08.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932430Ab2AJQuk (ORCPT ); Tue, 10 Jan 2012 11:50:40 -0500 Date: Tue, 10 Jan 2012 22:19:36 +0530 From: Vaidyanathan Srinivasan To: Arjan van de Ven Cc: Ingo Molnar , Suresh Siddha , Youquan Song , Peter Zijlstra , linux-kernel@vger.kernel.org, tglx@linutronix.de, hpa@zytor.com, akpm@linux-foundation.org, stable@vger.kernel.org, len.brown@intel.com, anhua.xu@intel.com, chaohong.guo@intel.com, Youquan Song Subject: Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken Message-ID: <20120110164936.GB17432@dirshya.in.ibm.com> Reply-To: svaidy@linux.vnet.ibm.com References: <1326099367-4166-1-git-send-email-youquan.song@intel.com> <1326103578.2442.50.camel@twins> <20120110001445.GA20542@linux-youquan.bj.intel.com> <1326107156.2442.59.camel@twins> <20120110055856.GA23741@linux-youquan.bj.intel.com> <1326153163.2366.7.camel@sbsiddha-mobl2> <20120110091805.GA28024@elte.hu> <4F0C4BF0.9090809@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <4F0C4BF0.9090809@linux.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) x-cbid: 12011006-5140-0000-0000-000000920DCE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Arjan van de Ven [2012-01-10 06:32:16]: > On 1/10/2012 1:18 AM, Ingo Molnar wrote: > > > > * Suresh Siddha wrote: > > > >> On Tue, 2012-01-10 at 00:58 -0500, Youquan Song wrote: > >>> Thanks Peter! Here is the patch. > >> > >> Youquan, As far as I know both the > >> sched_smt_power_savings/sched_mc_power_savings are broken for atleast an > >> year. > > > > We want a single knob, sched_power_savings - with the mc_ and > > smt_ ones still kept and aliased to sched_power_savings, for > > compatibility reasons. > > > > As Peter said, the other reasonable option is to have no knob at > > all and restart this code from scratch. > > > > The other thing we should do is to add sane defaults: to turn on > > sched_power_savings *AUTOMATICALLY* when a system is obviously > > battery driven and turn it off when the system is obviously AC > > driven. User-space can still implement policy and override the > > kernel's default, but there's absolutely no excuse to not offer > > this default ourselves. > > a very good default would be to keep all tasks on one package until half > the cores in the package are busy, and then start spreading out. > > I suspect that'll be the 90% case coverage. This is a good default, but I guess we will not consolidate tasks into SMT threads by default since that will be a larger performance drop. --Vaidy