From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753923AbcGDUmh (ORCPT ); Mon, 4 Jul 2016 16:42:37 -0400 Received: from www.linutronix.de ([62.245.132.108]:60266 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753753AbcGDUme (ORCPT ); Mon, 4 Jul 2016 16:42:34 -0400 Date: Mon, 4 Jul 2016 22:40:21 +0200 (CEST) From: Thomas Gleixner To: Vladimir Panteleev cc: Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, LKML , Peter Zijlstra Subject: Re: Subject: PROBLEM: CPU accounting/scheduling regression in v4.6 CPU scheduling patchset? In-Reply-To: <169481048.20160703172411@gmail.com> Message-ID: References: <169481048.20160703172411@gmail.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 3 Jul 2016, Vladimir Panteleev wrote: > Since updating my PC to Linux 4.6, I noticed the following problems: > > 1. CPU-bound tasks which use all CPU cores have a severe impact on > responsiveness. For example, the following bash command (which > simply starts one busyloop per core) is enough to make the machine > almost completely unresponsive: > > for N in $(seq $(nproc)) ; do while true ; do ; done & ; done > > 2. Nearly all tasks in the process listing are shown with 0% CPU > usage, even when they're CPU-bound. The only exceptions are the > kernel migration and kthreadd tasks, and occasionally the init > process. > > I have bisected the problem to commit > 1cf4f629d9d246519a1e76c021806f2a51ddba4d ("cpu/hotplug: Move online > calls to hotplugged cpu"), which is part of Thomas Gleixner's CPU > hotplug refactoring patchset [1]. It introduces both problems > described above. I doubt that, but that commit has been a bisect victim before ... > My system is a GIGABYTE X79S-UP5-WIFI motherboard (F5f BIOS) with an > i7-4960X CPU, running Arch Linux. I've reproduced with both the > distro's kernel config [2], as well as a minimal config for my > system. I can reproduce the problems on the latest rc at the moment, > v4.7-rc5. > > Comparing dmesg output before and after 1cf4f629, I see no notable > differences. > > I noticed an existing thread "S3 resume regression" [3] referencing > this commit, however it describes a different problem. I also found a > Bugzilla issue for the zero CPU usage problem [4], however it has no > replies. That one says: * After an hour or less (I have no idea), the top/ps start working * I do have exactly the same problem with the LTS branch 4.4.14 * With 4.5.4 I cannot reproduce the problem just after booting I tried to reproduce the issue on a couple of machines, but no luck. No idea at the moment, but Cc'ed scheduler folks. Thanks, tglx