linux-kernel - Re: HPET regression in 2.6.26 versus 2.6.25 -- question about NMI watchdog

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Message-ID: <20080815132646.GF30597@elte.hu>
Date:	Fri, 15 Aug 2008 15:26:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Witbrodt <dawitbro@...global.net>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>, linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, netdev <netdev@...r.kernel.org>
Subject: Re: HPET regression in 2.6.26 versus 2.6.25 -- question about NMI
	watchdog

* David Witbrodt <dawitbro@...global.net> wrote:

> Quick question: a quick browse of 'Documentation/nmi_watchdog.txt' 
> suggests that I should use "nmi_watchdog=1", since I have SMP (CPU = 
> Athlon 64 X2, with CONFIG_SMP=y).  Should I follow your suggestion 
> later, or follow the recommendation of the 'nmi_watchdog.txt' doc?

you could try both, starting with nmi_watchdog=2 - and trying 
nmi_watchdog=1 if that doesnt work. The problem with nmi_watchdog=1 is 
that it disables high-res timers. (because it has to - it piggy-backs on 
the back of a periodic timer interrupt)

you might even want to test the NMI watchdog with an intentional 
user-space hard lockup - with the attached lockupcli.c program. 
(Warning: if you run it as root it will really lock up your box hard. 
Run it from a VGA text mode console to see any console messages.)

	Ingo

View attachment "lockupcli.c" of type "text/plain" (47 bytes)