From mboxrd@z Thu Jan 1 00:00:00 1970 From: Erik Slagter Subject: Re: No c2-c7 states on core i7 Date: Mon, 23 Nov 2009 20:26:53 +0100 Message-ID: <4B0AE1FD.4030108@slagter.name> References: <4B06A7A8.109@slagter.name> <1258945512.3773.33.camel@localhost.localdomain> <4B0A4D62.2040001@slagter.name> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from eriks.xs4all.nl ([83.160.41.216]:44780 "EHLO eriks.xs4all.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754457AbZKWT0v (ORCPT ); Mon, 23 Nov 2009 14:26:51 -0500 In-Reply-To: Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Len Brown , ykzhao Cc: linux-acpi@vger.kernel.org > No, that isn't normal. C-states on modern processors generally > save a lot of energy. > > If you run powertop and you find that you are over 99% idle > and you save no energy compared to when you are 0% idle > (say a copy of "cat /dev/zero> /dev/null" for each core) > then something is wrong with your system. I just removed a large story here, I guess the table from my other message is a lot more informative. > It is possible, but as soon as you reverse engineer and over-ride > something in the BIOS, you are on very thin ice. Presumably > the BIOS engineer made a concious decision to disable C-states > when you over-clock your board and had a reason to do so. As long as nothing gets fried that's no problem for me. > Maybe the more important question is what measurable benefit > you get when you over-clock your board, and if you really need that... I can understand your doubts on this matter, but I think I do have a legitimate reasoning. This is a server that almost all of the time does next to nothing. Load 0.02 or similar. It needs to be running 24/24 though because it receives e-mail and answers the telephone. So that's why I want it to be low on power usage. On the other hand I need to transcode movie clips to h264 very regularly. I can use every 4*2 core for the process using x264 and indeed it works very fast. Also I noticed that every mhz higher clock means shorter encoding time, all (virtual-)cores get completely loaded. The "normal" speed of the 920 is 2.8 Ghz (or in fact 2.63 Ghz) and a change to 3.4 Ghz really does make a difference in encoding speed, theoretically 30%, in practise even more. Intel would really make me happy if they would design a processor with four or more cores and a chipset that would implement C7 and also could scale from 100 Mhz to 3.6 Ghz, in two or three steps, I wouldn't mind, and then would use something like 20 watts in idle, like my laptop does.