From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752282AbcHKXrj (ORCPT ); Thu, 11 Aug 2016 19:47:39 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:41612 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751676AbcHKXrg (ORCPT ); Thu, 11 Aug 2016 19:47:36 -0400 X-IBM-Helo: d03dlp02.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com Date: Thu, 11 Aug 2016 16:47:34 -0700 From: "Paul E. McKenney" To: Christoph Lameter Cc: Peter Zijlstra , Frederic Weisbecker , Chris Metcalf , Gilad Ben Yossef , Steven Rostedt , Ingo Molnar , Andrew Morton , Rik van Riel , Tejun Heo , Thomas Gleixner , Viresh Kumar , Catalin Marinas , Will Deacon , Andy Lutomirski , Daniel Lezcano , linux-doc@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: clocksource_watchdog causing scheduling of timers every second (was [v13] support "task_isolation" mode) Reply-To: paulmck@linux.vnet.ibm.com References: <7a3f66f7-5011-7d59-2e0e-f57e4e42e6b6@mellanox.com> <20160810221656.GC19757@lerouge> <20160811084002.GV30192@twins.programming.kicks-ass.net> <20160811160027.GV3482@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16081123-0012-0000-0000-000010616BAE X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00005579; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000181; SDB=6.00743392; UDB=6.00350048; IPR=6.00515936; BA=6.00004658; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00012317; XFM=3.00000011; UTC=2016-08-11 23:47:34 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16081123-0013-0000-0000-0000447A5630 Message-Id: <20160811234734.GJ3482@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-08-11_15:,, 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-1608110306 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 11, 2016 at 06:02:34PM -0500, Christoph Lameter wrote: > On Thu, 11 Aug 2016, Paul E. McKenney wrote: > > > > With modern Intel we could run it on one CPU per package I think, but at > > > the same time, too much in NOHZ_FULL assumes the TSC is indeed sane so > > > it doesn't make sense to me to keep the watchdog running, when it > > > triggers it would also have to kill all NOHZ_FULL stuff, which would > > > probably bring the entire machine down.. > > > > Well, you -could- force a very low priority CPU-bound task to run on > > all nohz_full CPUs. Not necessarily a good idea, but a relatively > > non-intrusive response to that particular error condition. > > Given that we want the cpu only to run the user task I would think that is > not a good idea. Heh! The only really good idea is for clocks to be reliably in sync. But if they go out of sync, what do you want to do instead? Thanx, Paul