From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752711AbcHLQTb (ORCPT ); Fri, 12 Aug 2016 12:19:31 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:35863 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752541AbcHLQT3 (ORCPT ); Fri, 12 Aug 2016 12:19:29 -0400 X-IBM-Helo: d03dlp02.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com Date: Fri, 12 Aug 2016 09:19:19 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: Christoph Lameter , Peter Zijlstra , 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> <20160811234734.GJ3482@linux.vnet.ibm.com> <20160812142611.GC5087@lerouge> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160812142611.GC5087@lerouge> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16081216-0016-0000-0000-00000468505C X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00005583; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000181; SDB=6.00743723; UDB=6.00350246; IPR=6.00516260; BA=6.00004660; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00012328; XFM=3.00000011; UTC=2016-08-12 16:19:25 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16081216-0017-0000-0000-000031F5967F Message-Id: <20160812161919.GV3482@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-08-12_07:,, 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-1608120170 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 12, 2016 at 04:26:13PM +0200, Frederic Weisbecker wrote: > On Fri, Aug 12, 2016 at 09:23:13AM -0500, Christoph Lameter wrote: > > On Thu, 11 Aug 2016, Paul E. McKenney wrote: > > > > > 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? > > > > For a NOHZ task? Write a message to the syslog and reenable tick. Fair enough! Kicking off a low-priority task would achieve the latter but not necessarily the former. And of course assumes that the worker thread is at real-time priority with various scheduler anti-starvation features disabled. > Indeed, a strong clocksource is a requirement for a full tickless machine. No disagrement here! ;-) Thanx, Paul