From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: CpuFreq Laptop Scaling broken? Date: Mon, 25 Aug 2014 19:26:03 +0530 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: linux-rt-users@vger.kernel.org, Thomas Gleixner , Steven Rostedt To: Harry van Haaren , "Rafael J. Wysocki" Return-path: Received: from mail-oa0-f43.google.com ([209.85.219.43]:34462 "EHLO mail-oa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755489AbaHYN4D (ORCPT ); Mon, 25 Aug 2014 09:56:03 -0400 Received: by mail-oa0-f43.google.com with SMTP id i7so10752232oag.2 for ; Mon, 25 Aug 2014 06:56:03 -0700 (PDT) In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: Fixing Rafael's id.. On 25 August 2014 19:25, Viresh Kumar wrote: > On 25 August 2014 17:58, Harry van Haaren wrote: >> I'm attempting to squeeze the lowest audio-latency out of a laptop as possible, >> and in doing so would like to set the CPU to performance. >> >> CPU in laptop: Intel(R) Core(TM)2 Duo CPU T7300 @ 2.00GHz >> >> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors >> ondemand performance >> >> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver >> acpi-cpufreq >> >> # Attempt to set performance governer >> $ echo "performance" >/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor >> bash: echo: write error: Invalid argument >> >> # Attempt to set min freq of 2GHz (max) of this core2duo >> $ echo 2000000 > /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq >> bash: /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq: Permission denied > > You tried both these as root? Even 'sudo' may not work.. > > I haven't seen the rt code since sometime, what tag should I look at ? > > I don't think there should be any such issues there.. > >> As far as I can tell, it is currently impossible on the -rt kernel to >> change CPU governer? >> This is necessary for reliable low-latency audio for laptop musicians. >> >> What is necessary to fix cpufreq on -rt? Cheers, -Harry >> >> PS: I've CC'd maintainers of cpufreq, I hope that's OK, otherwise >> please inform me of >> normal practices on linux-rt-users ML > > That's fine I suppose.