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Date: Thu, 4 Sep 2008 17:24:53 -0400
From: Don Zickus <dzickus@redhat.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: "Mingarelli, Thomas" <Thomas.Mingarelli@hp.com>,
       Andi Kleen <andi@firstfloor.org>, Ingo Molnar <mingo@elte.hu>,
       Prarit Bhargava <prarit@redhat.com>,
       Peter Zijlstra <peterz@infradead.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "arozansk@redhat.com" <arozansk@redhat.com>,
       "ak@linux.intel.com" <ak@linux.intel.com>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, "H. Peter Anvin" <hpa@zytor.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       "Maciej W. Rozycki" <macro@linux-mips.org>
Subject: Re: [PATCH RFC] NMI Re-introduce un[set]_nmi_callback
Message-ID: <20080904212453.GR3400@redhat.com>
References: <87y727vrgu.fsf@basil.nowhere.org> <20080904172052.GN3400@redhat.com> <20080904175231.GH18288@one.firstfloor.org> <20080904182637.GP3400@redhat.com> <20080904190816.GB4349@redhat.com> <20080904200032.GM18288@one.firstfloor.org> <183C1D5A376DE343AA8F94FC2A1EC14938D3E74841@GVW1091EXB.americas.hpqcorp.net> <20080904205725.GC4349@redhat.com> <183C1D5A376DE343AA8F94FC2A1EC14938D3E748D1@GVW1091EXB.americas.hpqcorp.net> <20080904212134.GD4349@redhat.com>
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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