linux-kernel - Re: [PATCH] watchdog: nohz: don't run watchdog on nohz

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Message-ID: <alpine.DEB.2.11.1503310514050.12306@gentwo.org>
Date:	Tue, 31 Mar 2015 05:17:19 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Chris Metcalf <cmetcalf@...hip.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Don Zickus <dzickus@...hat.com>,
	Andrew Jones <drjones@...hat.com>,
	chai wen <chaiw.fnst@...fujitsu.com>,
	Ingo Molnar <mingo@...nel.org>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Fabian Frederick <fabf@...net.be>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ben Zhang <benzh@...omium.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] watchdog: nohz: don't run watchdog on nohz_full cores

On Mon, 30 Mar 2015, cmetcalf@...hip.com wrote:

> Running watchdog can be a helpful debugging feature on regular
> cores, but it's incompatible with nohz_full, since it forces
> regular scheduling events.  Accordingly, just exit out immediately
> from any nohz_full core.

At this point we still have a timer tick every second. So just change the
way the checking occurs that it can be done during the once per second
tick for now? If the tick idle period is expanded later maybe only run the
watchdog activity during those inevitable ticks?

It may be best if the watchdog could be configured as to which processors
it should run on?

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