Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755325AbYATSYe (ORCPT ); Sun, 20 Jan 2008 13:24:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754152AbYATSYZ (ORCPT ); Sun, 20 Jan 2008 13:24:25 -0500 Received: from idcmail-mo1so.shaw.ca ([24.71.223.10]:43772 "EHLO pd4mo3so.prod.shaw.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753578AbYATSYY (ORCPT ); Sun, 20 Jan 2008 13:24:24 -0500 Date: Sun, 20 Jan 2008 12:24:09 -0600 From: Robert Hancock Subject: Re: PROBLEM: Celeron Core In-reply-to: To: David Newall Cc: Andi Kleen , Matt Mackall , Chodorenko Michail , Linux Kernel Mailing List Message-id: <479391C9.9020004@shaw.ca> MIME-version: 1.0 Content-type: text/plain; charset=ISO-8859-1; format=flowed Content-transfer-encoding: 7bit References: User-Agent: Thunderbird 2.0.0.9 (Windows/20071031) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1285 Lines: 27 David Newall wrote: > Andi Kleen wrote: >>> Isn't it the case that an idle machine will use >>> less power when throttled than when not? >>> >> No that is not the case (not even on old CPUs) >> > Then why would it run cooler? What generates the heat when not > throttled? What stops generating heat when throttled? And you say this > happens without reducing power consumption? I'm not convinced. I'm a > long way from that. I believe that all throttling does is forcibly halt the CPU on a particular duty cycle. This will reduce the rate of power consumption, but reduces the CPU performance by a greater amount (since even at 100% halted the CPU still consumes power) and so actually reduces performance per watt. It will spread the heat and power usage produced from a given workload task out in time (thus its usefulness in limiting CPU temperature) but will consume more power overall. Real CPU clock throttling schemes like SpeedStep, PowerNow, etc. actually do increase performance per watt when they kick in. -- 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/