From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752830AbZKGUwz (ORCPT ); Sat, 7 Nov 2009 15:52:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752776AbZKGUwz (ORCPT ); Sat, 7 Nov 2009 15:52:55 -0500 Received: from cantor.suse.de ([195.135.220.2]:46402 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750996AbZKGUwy (ORCPT ); Sat, 7 Nov 2009 15:52:54 -0500 From: Thomas Renninger To: "Luis R. Rodriguez" Subject: Re: [PATCH] cpu-freq: add troubleshooting section for FSB changes Date: Sat, 7 Nov 2009 21:52:56 +0100 User-Agent: KMail/1.9.10 Cc: davej@redhat.com, cpufreq@vger.kernel.org, linux-kernel@vger.kernel.org, mcgrof@gmail.com, Matthew Garrett , "Arjan van de Ven\"" , Reinette Chatre , Aeolus Yang , Amod Bodas , David Quan , Kishore Jotwani References: <1257537660-5301-1-git-send-email-lrodriguez@atheros.com> In-Reply-To: <1257537660-5301-1-git-send-email-lrodriguez@atheros.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200911072152.57596.trenn@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 06 November 2009 09:01:00 pm Luis R. Rodriguez wrote: > With cpu frequency scaling you may run into some system > performance issues when the FSB changes speed due to the > throughput constraints this brings on the system. Interesting. Could you be a bit more detailed how and what kind of perfomance issues are seen, please. I expect IO based issues like WLAN package throughput or even lost connections :) "wireless" is also a good word to grep for... If this gets documented also a bit more info about the HW should get added. The problem sounds rather restricted to specific models (atom based, laptop, desktop chipsets?)? Otherwise everyone adding a 10G network card into his Intel machine will start measuring or excluding the lowest freq when reading this. Thanks for the valuable info, Thomas > Document how to rule out whether or not FSB changes > affect general system issues. > > Cc: Matthew Garrett > Cc: Arjan van de Ven" > Cc: Reinette Chatre > Cc: Aeolus Yang > Cc: Amod Bodas > Cc: David Quan > Cc: Kishore Jotwani > Signed-off-by: Luis R. Rodriguez > --- > Documentation/cpu-freq/user-guide.txt | 45 > +++++++++++++++++++++++++++++++++ 1 files changed, 45 insertions(+), 0 > deletions(-) > > diff --git a/Documentation/cpu-freq/user-guide.txt > b/Documentation/cpu-freq/user-guide.txt index 2a5b850..846729d 100644 > --- a/Documentation/cpu-freq/user-guide.txt > +++ b/Documentation/cpu-freq/user-guide.txt > @@ -32,6 +32,7 @@ Contents: > 3. How to change the CPU cpufreq policy and/or speed > 3.1 Preferred interface: sysfs > > +4. Troubleshooting > > > 1. Supported Architectures and Processors > @@ -211,3 +212,47 @@ scaling_setspeed. By "echoing" a new frequency into > this you can change the speed of the CPU, > but only within the limits of > scaling_min_freq and scaling_max_freq. > + > +4. Troubleshooting > +================== > + > +If you are not sure if frequency scaling is the culprit to your > +issues you can try to disable the feature on the BIOS if possible. > + > +Alternatively it helps to understand that on some CPUs (Intel) > +the Front Side Bus (FSB) speed is changed when you happen to change > +the active CPU frequency to the lowest supported frequency, which > +happens to be the frequency used on the highest supported P-n state. > +The P0 state is the highest Performance state with the highest > +CPU frequency and system power. The highest P-n state would be > +the one with the lowest supported frequency and power. > + > +On Intel CPUs the FSB will not be modified with SpeedStep enabled if the > +second to last lowest frequency on the available scaling frequencies > +is used. Testing this would rule out whether or not the FSB changes > +made by SpeedStep would be the main issue. > + > +Modifying the FSB will alter your general system throughput > +on your Northbridge so to prevent general throughput issues > +with devices on it you can modify frequency scaling so that > +it nevers uses the lowest supported frequency. > + > +For example: > + > +cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_available_frequencies > +1801000 1800000 1200000 800000 > +1801000 1800000 1200000 800000 > + > +cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_min_freq > +800000 > +800000 > + > +To disable changing the FSB select the second to last CPU freq > +on the available freq for each CPU and set the scaling_min_freq > +for each CPU to that value. For the example output this would be > +echo'ing 1200000 to each scaling_min_freq: > + > +echo 1200000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq > +echo 1200000 > /sys/devices/system/cpu/cpu1/cpufreq/scaling_min_freq > + > +The first line is for the 1st CPU, the second line for the second line.