Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755092Ab1DEPBt (ORCPT ); Tue, 5 Apr 2011 11:01:49 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:54349 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755047Ab1DEPBp convert rfc822-to-8bit (ORCPT ); Tue, 5 Apr 2011 11:01:45 -0400 Subject: Re: cpuidle asymmetry (was Re: [RFC PATCH V4 5/5] cpuidle: cpuidle driver for apm) From: Peter Zijlstra To: dipankar@in.ibm.com Cc: Len Brown , Vaidyanathan Srinivasan , Trinabh Gupta , arjan@linux.intel.com, Stephen Rothwell , suresh.b.siddha@intel.com, benh@kernel.crashing.org, venki@google.com, ak@linux.intel.com, linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com In-Reply-To: <20110404143259.GA11525@in.ibm.com> References: <20110323121458.ec7cdaf9.sfr@canb.auug.org.au> <4D89CA7D.8080108@linux.vnet.ibm.com> <4D8B550D.5000409@linux.vnet.ibm.com> <20110325180156.GC19214@dirshya.in.ibm.com> <1301577536.4859.249.camel@twins> <1301666556.4859.695.camel@twins> <20110404143259.GA11525@in.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Tue, 05 Apr 2011 17:01:32 +0200 Message-ID: <1302015692.2225.1347.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1416 Lines: 32 On Mon, 2011-04-04 at 20:02 +0530, Dipankar Sarma wrote: > On Fri, Apr 01, 2011 at 04:02:36PM +0200, Peter Zijlstra wrote: > > > > > S0i3 on cpu0 can be entered only after cpu1 is already off-line, > > > among other system hardware dependencies... > > > > > > So it makes no sense to export S0i3 as a c-state on cpu1. > > > > > > When cpu1 is online, the scheduler treats it as a normal SMP. > > > > Dipankar's reply seems to address this issue well. > > I can't find any Moorestown documentation at the Intel site, but > thinking about Len's inputs a bit more, it seems there may > be still a problem asymetry from the scheduler perspective. > > If cpu0 or cpu1 either of them can be offlined, there is no > asymetry. If only cpu1 can be offlined, it would mean that > one cpu may be more efficient depending on how we do > cpu offlining for power savings. It gets a bit messy. > > Len, what exacty is the significance of offlining here ? > Apart from going to C6, what else is needed in cpu1 for > the chip to go to S0i3 ? Why is idle C6 not enough ? I don't think offlining is relevant, anybody using that for power management is doing it wrong, _very_ wrong. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/