linux-kernel - Re: clocksource_watchdog causing scheduling of timers every second (was [v13] support "task

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Message-ID: <20160812142611.GC5087@lerouge>
Date:	Fri, 12 Aug 2016 16:26:13 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Chris Metcalf <cmetcalf@...lanox.com>,
	Gilad Ben Yossef <giladb@...lanox.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Andy Lutomirski <luto@...capital.net>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-doc@...r.kernel.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: clocksource_watchdog causing scheduling of timers every second
 (was [v13] support "task_isolation" mode)

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.

Indeed, a strong clocksource is a requirement for a full tickless machine.