From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758706AbcHDOPN (ORCPT ); Thu, 4 Aug 2016 10:15:13 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:54559 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756606AbcHDOPI (ORCPT ); Thu, 4 Aug 2016 10:15:08 -0400 X-IBM-Helo: d01dlp01.pok.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com Date: Wed, 3 Aug 2016 09:16:31 -0700 From: "Paul E. McKenney" To: Rich Felker Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org, tglx@linutronix.de Subject: Re: rcu_sched stalls in idle task introduced in pre-4.8? Reply-To: paulmck@linux.vnet.ibm.com References: <20160802170414.GA20083@brightrain.aerifal.cx> <20160802181636.GJ3482@linux.vnet.ibm.com> <20160802192036.GW15995@brightrain.aerifal.cx> <20160802194802.GK3482@linux.vnet.ibm.com> <20160802203217.GZ15995@brightrain.aerifal.cx> <20160802204504.GL3482@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160802204504.GL3482@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16080414-0056-0000-0000-000000F748EF X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00005547; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000178; SDB=6.00739908; UDB=6.00347936; IPR=6.00512506; BA=6.00004644; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00012152; XFM=3.00000011; UTC=2016-08-04 14:14:06 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16080414-0057-0000-0000-000005118950 Message-Id: <20160803161631.GA20790@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-08-04_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1608040155 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 02, 2016 at 01:45:04PM -0700, Paul E. McKenney wrote: > On Tue, Aug 02, 2016 at 04:32:17PM -0400, Rich Felker wrote: > > On Tue, Aug 02, 2016 at 12:48:02PM -0700, Paul E. McKenney wrote: [ . . . ] > > > Does the problem reproduces easily? > > > > Yes, it happens right after boot and repeats every 30-90 seconds or > > so. > > Well, that at least makes it easier to test any patches! > > > > A bisection might be very helpful. > > > > Bisection would require some manual work to setup because the whole > > reason I was rebasing on Linus's tree was to adapt the drivers to > > upstream infrastructure changes (the new cpuhp stuff replacing > > notifier for cpu starting). The unfortunate way it was done, each > > driver adds an enum to linux/cpuhotplug.h so all the patches have > > gratuitous conflicts. In addition, for older revisions in Linus's > > tree, there's at least one show-stopping (hang during boot) bug that > > needs a cherry-pick to fix. There may be other small issues too. I > > don't think they're at all insurmountible but it requires an annoying > > amount of scripting. > > I had to ask! Might eventually be necessary, but let's see what we > can learn from what you currently have. And at first glance, my overnight run looks uglier than I would expect. I am now running tests at v4.7, and will run other tests to see if there really is a statistically significant degradation. If there is, then I might be able to bisect, though with nine-hour runs this could take quite some time. Thanx, Paul