Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761293Ab2FEBX0 (ORCPT ); Mon, 4 Jun 2012 21:23:26 -0400 Received: from mga09.intel.com ([134.134.136.24]:15985 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757358Ab2FEBXZ (ORCPT ); Mon, 4 Jun 2012 21:23:25 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,352,1309762800"; d="scan'208";a="148244921" Message-ID: <4FCD5F88.6050502@linux.intel.com> Date: Mon, 04 Jun 2012 18:23:20 -0700 From: Arjan van de Ven User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Rusty Russell CC: Peter Zijlstra , Thomas Gleixner , Fenghua Yu , Ingo Molnar , H Peter Anvin , Suresh B Siddha , Tony Luck , Asit K Mallick , linux-kernel , x86 , linux-pm , "Srivatsa S. Bhat" Subject: Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi References: <1338833876-29721-1-git-send-email-fenghua.yu@intel.com> <1338842001.28282.135.camel@twins> <87zk8iioam.fsf@rustcorp.com.au> In-Reply-To: <87zk8iioam.fsf@rustcorp.com.au> X-Enigmail-Version: 1.4.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1934 Lines: 41 On 6/4/2012 5:40 PM, Rusty Russell wrote: > On Mon, 04 Jun 2012 22:33:21 +0200, Peter Zijlstra wrote: >> On Mon, 2012-06-04 at 22:11 +0200, Thomas Gleixner wrote: >> >>> I understand what you are trying to do, though I completely disagree >>> with the solution. >>> >>> The main problem of the current hotplug code is that it is an all or >>> nothing approach. You have to tear down the whole thing completely >>> instead of just taking it out of the usable set of cpus. >>> >>> I'm working on a proper state machine driven online/offline sequence, >>> where you can put the cpu into an intermediate state which avoids >>> bringing it down completely. This is enough to get the full >>> powersaving benefits w/o having to go through all the synchronization >>> states of a full online/offline. That will shorten the onlining time >>> of an previously offlined cpu to almost nothing. >>> >>> I really want to avoid adding more bandaids to the hotplug code before >>> we have sorted out the existing horror. >> >> Its far worse.. you shouldn't _ever_ care about hotplug latency unless >> you've got absolutely braindead hardware. We all now ARM has been >> particularly creative here, but is Intel now trying to trump ARM at >> stupid? > > I disagree. Deactivating a cpu for power saving is halfway to hotplug > anyway. I'd rather unify the two cases, where we can specify how dead a > CPU should be, than have individual archs and boards do random hacks. well on PC's there really is no difference at least; idle equals "all power removed" already there. but I can see that on some other architectures, that lack idle that deep, there can be a real difference. -- 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/