Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759042Ab1CCWnD (ORCPT ); Thu, 3 Mar 2011 17:43:03 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:62854 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759019Ab1CCWnA (ORCPT ); Thu, 3 Mar 2011 17:43:00 -0500 X-Authority-Analysis: v=1.1 cv=+c36koQ5Dcj/1qolKHjtkYAGXvrVJRRiKMp+84F5sLg= c=1 sm=0 a=udRi0BhUxgIA:10 a=Q9fys5e9bTEA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=x7NVS_Hyu7oks7qMQ2QA:9 a=kg0vsNl7OoFLDyGGC9fxIx8--FcA:4 a=PUjeQqilurYA:10 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Subject: Re: [PATCH V6 0/2] tracing, perf: cpu hotplug trace events From: Steven Rostedt To: Thomas Renninger Cc: Vincent Guittot , Ingo Molnar , linux-kernel@vger.kernel.org, linux-hotplug@vger.kernel.org, fweisbec@gmail.com, amit.kucheria@linaro.org, rusty@rustcorp.com.au, tglx@linutronix.de, Arjan van de Ven , Alan Cox , Peter Zijlstra , "H. Peter Anvin" , Andrew Morton , linux-perf-users@vger.kernel.org In-Reply-To: <201103022307.46694.trenn@suse.de> References: <201103021157.08260.trenn@suse.de> <201103022307.46694.trenn@suse.de> Content-Type: text/plain; charset="ISO-8859-15" Date: Thu, 03 Mar 2011 17:42:56 -0500 Message-ID: <1299192176.6376.47.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 953 Lines: 23 On Wed, 2011-03-02 at 23:07 +0100, Thomas Renninger wrote: > I doubt cpu offlining is the proper instrument to save power. > You want to prevent the CPU of being used by ripping it out from scheduler decisions and > make sure it doesn't get interrupts by offlining. But the (latency) price is high. I could imagine that a server could use this for power savings to take down all but 1 CPU on off hours. When it knows its not going to get much action but still needs to remain online. Then just before peak times begin, online the other CPUs. But anything more dynamic than that, I can't see it really worth it. As the latency to bring the other CPU online, may miss a peak when it was needed. -- Steve -- 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/