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

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Date:	Fri, 15 Aug 2008 05:49:17 -0700 (PDT)
From:	David Witbrodt <dawitbro@...global.net>
To:	Ingo Molnar <mingo@...e.hu>
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



> > I found something very interesting about the commit that first causes 
> > the lockup (3def3d6d...), and the very next commit (1e934dda...) -- if 
> > I checkout 1e94... and try to revert the changes made in 3def..., the 
> > kernel freezes in spite of the revert.
> > 
> > Because of this, I would conclude that your patch for 2.6.27-rc3 was 
> > doomed before you began, and we should look more carefully at the 
> > commits from February instead of trying to revert at the 2.6.27 HEAD.
> 
> i'm still wondering whether we could try to figure out something about 
> the nature of the hard lockup itself.
> 
> Have you tried to activate the NMI watchdog? It _usually_ works fine if 
> you use a boot option along the lines of:
> 
>    "lapic nmi_watchdog=2 idle=poll"

I have to go to work for a few hours right now, but will try this out when
I get home.  (Actually, I'm late for work as I type this... but I have my
priorities straight!  ;)

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?


Much thanks,
Dave W.
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