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Message-ID: <3AAC8862.3461A1A8@mvista.com>
Date: Mon, 12 Mar 2001 00:27:14 -0800
From: george anzinger <george@mvista.com>
Organization: Monta Vista Software
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To: Keith Owens <kaos@ocs.com.au>
CC: mingo@elte.hu, Andrew Morton <andrewm@uow.edu.au>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: [patch] serial console vs NMI watchdog
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Keith Owens wrote:
> 
> On Sun, 11 Mar 2001 20:43:16 -0800,
> george anzinger <george@mvista.com> wrote:
> >Consider this.  Why not use the NMI to sync the cpus.  Kdb would have a
> >function that is called each NMI.
> 
> kdb uses NMI IPI to get the other cpu's attention.  One cpu is in
> control and may or may not be accepting NMI, it depends on the event
> that entered kdb.  The other cpus end up in kdb code, spinning waiting
> for a cpu switch.  Initially they are not receiving NMI because they
> were invoked via NMI which is masked until they exit.  However if the
> user does a cpu switch then single steps the interrupted code, the cpu
> has to return from the NMI handler to the interrupted code at which
> time this cpu starts receiving NMI again.

Are you actually twiddling the hardware, or just changing what happens
on NMI?
> 
> The kdb context can change from ignoring NMI to accepting NMI.  It is
> easier to bring all the cpus into kdb and let the kdb code decide if it
> ignores any NMI that is being received.

Yes. Exactly.

George
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