From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fernando Lopez-Lezcano Subject: Re: CpuFreq Laptop Scaling broken? Date: Mon, 25 Aug 2014 10:18:30 -0700 Message-ID: <53FB6FE6.30408@localhost> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: nando@ccrma.Stanford.EDU, linux-rt-users@vger.kernel.org, Thomas Gleixner , Steven Rostedt , rjw@rjwysocki.net To: Harry van Haaren , Viresh Kumar Return-path: Received: from smtp1.Stanford.EDU ([171.67.219.81]:45809 "EHLO smtp.stanford.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932187AbaHYR2d (ORCPT ); Mon, 25 Aug 2014 13:28:33 -0400 In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: On 08/25/2014 07:02 AM, Harry van Haaren wrote: > On Mon, Aug 25, 2014 at 2:55 PM, Viresh Kumar wrote: >> You tried both these as root? Even 'sudo' may not work.. > Yes, the original output was all as root (not sudo, genuine root). > >> I haven't seen the rt code since sometime, what tag should I look at ? > I'm running 3.14.12-rt9-1-rt (as packaged for Arch here: > https://aur.archlinux.org/packages/linux-rt ) Hi Harry, Check to see if you see something in /sys/devices/system/cpu/intel_pstate/ If so then the intel pstate driver is what is controlling cpu speed for you (that changed since 3.9 or so). You can set min_perf_pct to "100" to set your minimum cpu speed to the maximum possible. Even then you will see some variation but in my usage case jackd is again usable after this change[*]. See: https://wiki.archlinux.org/index.php/CPU_frequency_scaling -- Fernando [*] I think the intel pstate drive is not yet aware of what the scheduler does with tasks (or visceversa). In the case of jackd I think that the scheduler can move a task to a processor that is throttled down and the change in speed after detecting high load does not happen fast enough. Jackd runs out of cpu cycles and you get an xrun. By the next jackd cycle the cpu is running up to speed and everything is fine but the task might be moved again to a different core. Just speculation on my part.