linux-kernel - Re: [PATCH RFC] NMI Re-introduce un[set]_nmi

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Message-ID: <20080904212453.GR3400@redhat.com>
Date:	Thu, 4 Sep 2008 17:24:53 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"Mingarelli, Thomas" <Thomas.Mingarelli@...com>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Prarit Bhargava <prarit@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arozansk@...hat.com" <arozansk@...hat.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: [PATCH RFC] NMI Re-introduce un[set]_nmi_callback

On Thu, Sep 04, 2008 at 05:21:34PM -0400, Vivek Goyal wrote:
> On Thu, Sep 04, 2008 at 09:05:37PM +0000, Mingarelli, Thomas wrote:
> > Ok regarding question #1. The die_notifier works as you mentioned; however, the fact that the watchdog timer ticks also come through as NMIs is a hinderance. Now, when the watchdog timer is configured through the LOCAL_APIC the issue isn't so bad. I think the hpwdt driver handles the NMI coming in because there isn't a flood of timer ticks coming through as in the IOAPIC case.
> 
> Ok, so how does replacing the nmi callback help here? You driver handler
> be still called upon timer ticks. So you will be called on watchdog tick
> whether you are on die chain or you replace nmi handler with nmi callback.
> So watchdog ticks can't be a reason for not being on die chain.

Prarit's patch disabled the timer upon registering a callback to prevent
this case.  The thought was if you have your own handler you could provide
your own watchdog.

Cheers,
Don
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