From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dominik Brodowski Subject: Re: [PATCHSET] 0/3 Dynamic cpufreq governor and updates to ACPI P-state driver Date: Tue, 4 Nov 2003 08:16:38 +0100 Sender: cpufreq-bounces+glkc-cpufreq=gmane.org@www.linux.org.uk Message-ID: <20031104071638.GA4126@brodo.de> References: Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: cpufreq-bounces+glkc-cpufreq=gmane.org@www.linux.org.uk Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jan Rychter Cc: Mukesh Rajan , cpufreq@www.linux.org.uk, linux-acpi On Mon, Nov 03, 2003 at 07:21:34PM -0800, Jan Rychter wrote: > >>>>> "Len" == Len Brown writes: > >> I have done some measurements on a Toshiba S7/290LNKW, which has a > >> 900MHz Pentium-M. The results have been posted to this list a while > >> ago -- the most surprising one being that the Pentium-M in that > >> machine seemed to always consume the same amount of power when idle, > >> independent of operating frequency. The frequency only made a > >> difference when the CPU was actually doing something (or when I made > >> it not use the C3 state by loading usb-uhci). > > Len> Probably the cpu is running HLT in the idle loop, so the power > Len> consumption there would not vary with MHz. > > Oh -- well, that's exactly what I wanted to check. It seems it does vary > for speedstepped Pentium-III Mobile, according to my measurements, > that's why I was surprised. > > This should influence the design of dynamic power management -- if the > CPU is already idle, there is no point in slowing it down. It only makes > sense to change the frequency when we're actually doing something. This assumption is at least partly wrong. Pentium-III Mobile datasheets clearly show that the power usage when doing nothing varies up to 50% dependand on the frequency setting. So even if it is no measurable effect on one processor, this theory isn't true for all processors. And dynamic power management should work best _for all processors_. Dominik