From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id B4283687DE for ; Mon, 28 Nov 2005 13:58:20 +1100 (EST) From: Benjamin Herrenschmidt To: Paul Mackerras In-Reply-To: <17290.26688.710369.613144@cargo.ozlabs.ibm.com> References: <20051126113805.709ee538.pochini@shiny.it> <17290.26688.710369.613144@cargo.ozlabs.ibm.com> Content-Type: text/plain Date: Mon, 28 Nov 2005 13:52:48 +1100 Message-Id: <1133146369.7768.170.camel@gaston> Mime-Version: 1.0 Cc: LinuxPPC-dev Subject: Re: CPU off power consumption List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2005-11-28 at 13:15 +1100, Paul Mackerras wrote: > Giuliano Pochini writes: > > > Out of curiosity, what's the difference between a cpu that has never been > > enabled and one that has been disabled with echo 0>/sys/.../online ? It > > happens that when I boot with maxcpus=0 the temperature always stays low > > enoung that the fan never spins up. If I enable and then I immediately > > disable the 2nd cpu, the temperature goes a few degrees up. I have a dual > > G4-MDD. > > Interesting. A cpu that has been disabled will be in sleep mode with > interrupts disabled and its caches flushed. One that has never been > started may possibly be held in the reset state. The way to check > would be to check the state of the GPIO register that controls the > soft reset line of the second CPU. No, I think CPUs that have not been started are held in a similar sleep loop in ROM. I don't see right away why there would be any power consumption difference unless some bug causing us to never actually call the sleep loop .... Ben.