From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frederic Weisbecker Subject: Re: clocksource_watchdog causing scheduling of timers every second (was [v13] support "task_isolation" mode) Date: Sat, 13 Aug 2016 17:39:45 +0200 Message-ID: <20160813153942.GB21154@lerouge> References: <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> <20160812161919.GV3482@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20160812161919.GV3482-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: "Paul E. McKenney" 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-api@vger.kernel.org On Fri, Aug 12, 2016 at 09:19:19AM -0700, Paul E. McKenney wrote: > 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! ;-) I have a bot in my mind that randomly posts obvious statements about nohz_full here and then :-) From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752794AbcHMPjy (ORCPT ); Sat, 13 Aug 2016 11:39:54 -0400 Received: from mail-wm0-f47.google.com ([74.125.82.47]:36849 "EHLO mail-wm0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752653AbcHMPjv (ORCPT ); Sat, 13 Aug 2016 11:39:51 -0400 Date: Sat, 13 Aug 2016 17:39:45 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" 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) Message-ID: <20160813153942.GB21154@lerouge> References: <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> <20160812161919.GV3482@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160812161919.GV3482@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 12, 2016 at 09:19:19AM -0700, Paul E. McKenney wrote: > 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! ;-) I have a bot in my mind that randomly posts obvious statements about nohz_full here and then :-)