From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755281AbcI2C0x (ORCPT ); Wed, 28 Sep 2016 22:26:53 -0400 Received: from mail-oi0-f45.google.com ([209.85.218.45]:34958 "EHLO mail-oi0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754751AbcI2C0o (ORCPT ); Wed, 28 Sep 2016 22:26:44 -0400 Subject: Re: Regression in 4.8 - CPU speed set very low To: Lennart Sorensen References: <3919370.SGLjGupePs@vostro.rjw.lan> <075788ab-34e0-803c-f2b4-3f370ecc6b14@lwfinger.net> <2477506.olat0BX4ex@vostro.rjw.lan> <1436996d-078b-aa51-4452-b6655d917135@lwfinger.net> <20160927145114.GM14311@csclub.uwaterloo.ca> Cc: "Rafael J. Wysocki" , LKML , Linux PM list , Srinivas Pandruvada From: Larry Finger Message-ID: <8a5f37bb-4870-b89e-6287-fcb43b2e708f@lwfinger.net> Date: Wed, 28 Sep 2016 21:26:42 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20160927145114.GM14311@csclub.uwaterloo.ca> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/27/2016 09:51 AM, Lennart Sorensen wrote: > On Mon, Sep 26, 2016 at 04:28:29PM -0500, Larry Finger wrote: >> Mostly I use a KDE applet named "System load" and look at the "average >> clock", but the same info is also available in /proc/cpuinfo as "cpu MHz". >> When the bug triggers, the system gets very slow, and the cpu fan stops even >> though the cpu is still busy. >> >> Commit f7816ad, which had run for 7 days without showing the bug, failed >> after about 2 hours today. All my testing since Sept. 9 has been wasted. Oh >> well, that's the way it goes! > > Is it possible there is no bug and instead you have a hardware problem? > > What I am thinking: > > CPU fan stops, then CPU gets busy, CPU overheats, thermal throtling > kicks in to protect CPU and it gets VERY slow. > > So maybe you have a bad CPU fan that is getting stuck. Perhaps even if > you have a motherboard that varies the CPU fan depending on need and the > fan doesn't like the lowest speed and sometimes gets stuck when asked > to go slow. > > Of course if the CPU fan is the problem that could explain why it takes > varying amounts of time to see the problem. > > I suggest checking what the cpu temperature sensors are showing next > time it gets slow. By the time it gets slow, the CPU's cool, and one cannot see the temp just before that event happened. The reason I suspect a bug is that it fails with 4.8-rcX, but not with 4.7. Of course, it could be something subtle that slightly changes the heat load, which causes the CPU temp to be a little higher so that the effect is triggered. I am reasonably confident that it is not a hardware problem, but we may have to wait until 4.8 is released and gets wider usage. If no one else reports a problem, then I am certainly wrong. Larry