Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755703Ab2FERuv (ORCPT ); Tue, 5 Jun 2012 13:50:51 -0400 Received: from merlin.infradead.org ([205.233.59.134]:58548 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755585Ab2FERut convert rfc822-to-8bit (ORCPT ); Tue, 5 Jun 2012 13:50:49 -0400 Message-ID: <1338918625.2749.29.camel@twins> Subject: RE: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi From: Peter Zijlstra To: "Luck, Tony" Cc: "Yu, Fenghua" , Rusty Russell , Thomas Gleixner , Ingo Molnar , H Peter Anvin , "Siddha, Suresh B" , "Mallick, Asit K" , Arjan Dan De Ven , linux-kernel , x86 , linux-pm , "Srivatsa S. Bhat" Date: Tue, 05 Jun 2012 19:50:25 +0200 In-Reply-To: <3908561D78D1C84285E8C5FCA982C28F19300965@ORSMSX104.amr.corp.intel.com> References: <1338833876-29721-1-git-send-email-fenghua.yu@intel.com> <1338842001.28282.135.camel@twins> <87zk8iioam.fsf@rustcorp.com.au> <1338881971.28282.150.camel@twins> <3E5A0FA7E9CA944F9D5414FEC6C7122007727023@ORSMSX105.amr.corp.intel.com> <1338912565.2749.9.camel@twins> <3E5A0FA7E9CA944F9D5414FEC6C7122007728081@ORSMSX105.amr.corp.intel.com> <1338913190.2749.10.camel@twins> <3908561D78D1C84285E8C5FCA982C28F19300965@ORSMSX104.amr.corp.intel.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1313 Lines: 30 On Tue, 2012-06-05 at 17:44 +0000, Luck, Tony wrote: > > Like what? Offline is nothing more than a C state on x86. > > Offline is a bigger hammer than idle. > > When a core is idle it may take an interrupt which wakes it up to use power. > The scheduler may assign a process to run on it, which will wake it up to use power. > > When a core is offline we take extra steps (re-routing interrupts, telling the > scheduler it is not available for work) to make sure it STAYS in that low > power state. You also wreck cpusets, cpu affinity and you need some userspace crap to poll state trying to figure out when to wake up again. (And yes, I've heard stories about userspace hotplug daemons that cause machine wakeups themselves and were a main source of power usage at some point). All the timer/interrupt nonsense needs to be fixed anyhow, the HPC and RT people want isolation anyway. So shouldn't we all start by fixing the entire load-balancer/timer/interrupt madness before we start swinging stupid big hammers around that break half the interfaces we have? -- 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/