From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S268095AbUHWVhj (ORCPT ); Mon, 23 Aug 2004 17:37:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S268052AbUHWVcI (ORCPT ); Mon, 23 Aug 2004 17:32:08 -0400 Received: from mail.tmr.com ([216.238.38.203]:48143 "EHLO gatekeeper.tmr.com") by vger.kernel.org with ESMTP id S268017AbUHWVaC (ORCPT ); Mon, 23 Aug 2004 17:30:02 -0400 To: linux-kernel@vger.kernel.org Path: not-for-mail From: Bill Davidsen Newsgroups: mail.linux-kernel Subject: Re: SMP cpu deep sleep Date: Mon, 23 Aug 2004 17:30:29 -0400 Organization: TMR Associates, Inc Message-ID: References: <1092989207.18275.14.camel@linux.local> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Trace: gatekeeper.tmr.com 1093296221 21575 192.168.12.100 (23 Aug 2004 21:23:41 GMT) X-Complaints-To: abuse@tmr.com User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040803 X-Accept-Language: en-us, en In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Wes Felter wrote: > I worked on this last year (I call it CPU packing, because the idea is to > pack the load onto the fewest number of CPUs). > > The CPU hotplug patch is the way to go, but the hardware is the problem. I > talked to an Intel CPU architect at MICRO last year and he confirmed that > SMP Intel systems don't support any low-power modes besides HLT. AMD's > documentation says that Opterons support voltage/frequency scaling (aka > Cool 'n' Quiet), but AFAICT the documentation is wrong. In summary, you > are doomed. > For power saving, HLT is hard to beat ;-) You note HLT as if there was some good reason not to use it... Mask everything except some BACK2WORK int from the night watchman CPU. I would really like this on some machines which seem to leave all CPUs generating heat even when booted with a uni kernel. Whilst thinking about this, *if* using HLT is practical in therms of power saving, perhaps all but the last CPU could HLT if the run queue was empty, and only be awakened by the "last" CPU, in some case where the run queue length was longer than {some_value}. -- -bill davidsen (davidsen@tmr.com) "The secret to procrastination is to put things off until the last possible moment - but no longer" -me