From mboxrd@z Thu Jan 1 00:00:00 1970 From: Len Brown Subject: Re: No c2-c7 states on core i7 Date: Wed, 25 Nov 2009 01:59:55 -0500 (EST) Message-ID: References: <4B06A7A8.109@slagter.name> <1258945512.3773.33.camel@localhost.localdomain> <4B0A4D62.2040001@slagter.name> <4B0AE1FD.4030108@slagter.name> <20091124143459.385a0bc9@starbug.prg01.itonis.net> <4B0BE5B8.7060402@slagter.name> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: Received: from vms173019pub.verizon.net ([206.46.173.19]:56369 "EHLO vms173019pub.verizon.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752276AbZKYG7u (ORCPT ); Wed, 25 Nov 2009 01:59:50 -0500 Received: from localhost.localdomain ([74.104.151.18]) by vms173019.mailsrvcs.net (Sun Java(tm) System Messaging Server 6.3-7.04 (built Sep 26 2008; 32bit)) with ESMTPA id <0KTN006DUKRWLBD5@vms173019.mailsrvcs.net> for linux-acpi@vger.kernel.org; Wed, 25 Nov 2009 00:59:56 -0600 (CST) In-reply-to: <4B0BE5B8.7060402@slagter.name> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Erik Slagter Cc: Jindrich Makovicka , linux-acpi@vger.kernel.org > Yesterday I raised the clock to 3.4 Ghz and I set all voltages to "normal" and > it seems to run fine. I will have to check under really heavy load yet, I will > do that tonight. My motherboard has an option "power line load calibration", I > guess that has something to do with it :-) > > Interesting: I pulled out a "modern" (but cheapo, no fans) pcie vga card and > replaced it with a very old pci card (I guess from 1996) and that saves me 20 > watts! That's more power than I problably ever could save using C states! Yep, beware graphics card power. > BTW on my ancient athlon-mp board, I could enable c2/c3 (although not > supported by the bios) and that would save about ~40 watts of power. But it > looks I won't see such a difference on modern CPU's, maybe because of the > dynamic frequency scaling and enhanced c1? Is there anyone who can give me an > indication of what to expect in powersavings by c2-c7 on modern cpu's? On the mobile parts they used to publish the power limits for C-states, but I don't see these numbers in the core i7 datasheet... However, many have done comparisons of what you might expect for idle vs loaded power. eg. http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=3634&p=17 In general, I don't view it as a Linux bug that the MB's BIOS disables c-states when it is over-clocked. Indeed, it is quite possibly a BIOS feature. Len Brown, Intel Open Source Technology Center