linux-kernel - Re: troubleshooting/debugging hard locks

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Date:	Wed, 14 May 2008 17:42:58 -0600
From:	Zan Lynx <zlynx@....org>
To:	Ray Lee <ray-lk@...rabbit.org>
Cc:	Lee Howard <faxguy@...ardsilvan.com>, linux-kernel@...r.kernel.org
Subject: Re: troubleshooting/debugging hard locks

On Wed, 2008-05-14 at 15:43 -0700, Ray Lee wrote:
> On Wed, May 14, 2008 at 12:27 PM, Lee Howard <faxguy@...ardsilvan.com> wrote:

> >  But, without kernel messages indicating where to look to debug... what is
> > the best approach to start troubleshooting and debugging this condition?  Is
> > there some general debug feature that can be enabled in the kernel that
> > would help hone in on the culprit?
> 
> There's something called the NMI watchdog, that will print debugging
> messages out if it finds the system has hard locked. The short version
> is that you should add "nmi_watchdog=1" (no quotes) to the line in
> GRUB that has the kernel options. That assumes you have an APIC on the
> system. If that's not the case (you're on Uniprocessor, and no APIC)
> then you can try nmi_watchdog=2 instead. That'll only work on some
> systems, though.
> 
> Better docs (than my cheesy writeup) are in
> Documentation/nmi_watchdog.txt in the kernel source distribution.

I was once told to add these to the kernel command line as well when
using NMI watchdog and they do seem to help it trigger more reliably: 

"idle=poll nohz=off"

-- 
Zan Lynx <zlynx@....org>

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