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

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Message-ID: <551AE82C.7000101@ezchip.com>
Date:	Tue, 31 Mar 2015 14:32:12 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Don Zickus <dzickus@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	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>,
	Christoph Lameter <cl@...ux.com>,
	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 03/30/2015 10:04 PM, Mike Galbraith wrote:
> On Mon, Mar 30, 2015 at 02:51:05PM -0400, cmetcalf@...hip.com wrote:
>> From: Chris Metcalf <cmetcalf@...hip.com>
>>
>> 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.
> Hm, I don't see why this is needed, for debugging/testing you turn it
> on, when you set up for critical operation, you turn it off.

It can be helpful to keep the watchdog running even in production
to help diagnose hard-to-reproduce failures.  You just can't have it
running on the nohz_full cores.

-- 
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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