From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753287AbdBCNxO (ORCPT ); Fri, 3 Feb 2017 08:53:14 -0500 Received: from mout.gmx.net ([212.227.17.21]:60284 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752496AbdBCNxM (ORCPT ); Fri, 3 Feb 2017 08:53:12 -0500 Message-ID: <1486129955.3993.6.camel@gmx.de> Subject: Re: [tip:sched/core] sched/core: Add debugging code to catch missing update_rq_clock() calls From: Mike Galbraith To: Peter Zijlstra Cc: Sachin Sant , Ross Zwisler , Matt Fleming , Michael Ellerman , "linuxppc-dev@lists.ozlabs.org" , "linux-next@vger.kernel.org" , LKML , Paul McKenney Date: Fri, 03 Feb 2017 14:52:35 +0100 In-Reply-To: <20170203133748.GB6515@twins.programming.kicks-ass.net> References: <87tw8gutp6.fsf@concordia.ellerman.id.au> <20170130213435.GM31613@codeblueprint.co.uk> <33118425-8548-475A-8DED-9A2424C0BCCC@linux.vnet.ibm.com> <1485863317.4498.2.camel@gmx.de> <20170202155506.GX6515@twins.programming.kicks-ass.net> <3BAB5673-2BF8-46E0-8018-6A0F3DEEC9F7@linux.vnet.ibm.com> <20170203085301.GA6515@twins.programming.kicks-ass.net> <1486126774.4277.6.camel@gmx.de> <20170203133748.GB6515@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="us-ascii" X-Mailer: Evolution 3.16.5 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Provags-ID: V03:K0:gB2yLWZwKPk9W1xnTW1F5KvzIpdHrihnKknB6lXH7jXaSErMhHE fzjt/OcOkKJs0NU6dF3nv9BxMDUacrBfuHcYs7Xo/CaxFzfZVnIJ4lvRBOh4mX5IXBhCzuC HE3UGVZT70CqYf86GqQLbb/djmEAjrb3hRMtXhl9hBLgr4i7mxsEPSBUrOYrGktiH7hrg69 +/kC02eBP4kHCD2hgI4sw== X-UI-Out-Filterresults: notjunk:1;V01:K0:ANAmMaV8B4Y=:Q3ztR8YXv6xpCa0y+ZjReU lKy4+xvZYvZev7dBPZRWDBxWe/h9a5ULLVGcrxtK9w64DTSvbZgDO3WGym3J5uhLyTvRxfuEC k2jiGV/2juuGcpnkbInp9I3PaOiza39BXQZMOSgO/ELNs1wkKoLzQLND/iQlyHCyIB1GBu5ew 1qfE9JGmMQeffkaYgkEnFen03YYmrZDU7PnhNbbMrgEThAy1EhWZg4cWGr1T6XyjvfnIU6X/I nLn0OuPk9lWEvycMbT5ms6waDWATfPblMgIfIF11ixerjlo8JtqaqA519bKxthFUgLZhNgzXg KuPtLQCDHVuD6aBCc+C4dy9loTU/+RJT1BLSuCTavZ45y3hGdfkE/Gm8LQmRbFB4VtdQzxVk+ nvC/PN51iNX0nCjLcvO4dwPIwZkEbnhe5qsaFMq12JDQCBFO39MHrzr9+BfQYunGA89XGXtiO 9A1lns5yl731JXWI3mqy4XiDvJWyVA8+9u6Td8QGb/6fQZw16Perx4J0UpCaFgxUDmyxCgRng GK6KPzdQMYpXl768Bm89JdN8v2Sbm4siehFDHD0ibVJ+bQ79OfCWRx9kVy16IINoSoQYwA73f 6DX7vMZaW5U6b+2V/gVpj1UFQf2ZCp+T6qMz35FjT0B0gLw9TaovoY3q9is3dODoYmSAlytZa bcYe6xDxg2dPwzGLk/+1YCz+4nHKaTvW7+XQykYh/n1wmr/1ZPbctfsGgr5Z+IVwa4+JWDTod 9UEaZukKZXvGDmGKiOKif0T9p6nwA77cos8TP0cSvnb6YAVMyQ4rsM03ML/xcgxJNe2YYAqKz 4imaS2h9H988nq1KSKlb8bdpBtilfB2UKc1l9qw2lwwTOIKB5afbJ5re/GJNjgwYVJxRz/Cgw FrNwSJOkTniRSGpZ54/InXUkMBmWb10JfmYI2qgNtDouus8Xxu3zZYWqnPAcHb2m9vfr1Z/x4 aj8RrLs4xUNmicMDr4mZO0G/+on4NmoOGxw2Q7WkCcKO6OTYPb+epYjVbbLRI2sGpUbaMfET2 vsFnmKGcgYpeWHbsdk4GN4c= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2017-02-03 at 14:37 +0100, Peter Zijlstra wrote: > On Fri, Feb 03, 2017 at 01:59:34PM +0100, Mike Galbraith wrote: > > FWIW, I'm not seeing stalls/hangs while beating hotplug up in tip. (so > > next grew a wart?) > > I've seen it on tip. It looks like hot unplug goes really slow when > there's running tasks on the CPU being taken down. > > What I did was something like: > > taskset -p $((1<<1)) $$ > for ((i=0; i<20; i++)) do while :; do :; done & done > > taskset -p $((1<<0)) $$ > echo 0 > /sys/devices/system/cpu/cpu1/online > > And with those 20 tasks stuck sucking cycles on CPU1, the unplug goes > _really_ slow and the RCU stall triggers. What I suspect happens is that > hotplug stops participating in the RCU state machine early, but only > tells RCU about it really late, and in between it gets suspicious it > takes too long. Ah. I wasn't doing a really hard pounding, just running a couple instances of Steven's script. To beat hell out of it, I add futextest, stockfish and a small kbuild on a big box. -Mike