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Re: KDB on SMP machines

To: Corey Minyard <cminyard@xxxxxxxxxx>
Subject: Re: KDB on SMP machines
From: Jim Houston <jim.houston@xxxxxxxxx>
Date: Thu, 21 Nov 2002 12:53:41 -0500
Cc: kdb@xxxxxxxxxxx
References: <3DDD0473.70602@xxxxxxxxxx>
Reply-to: jim.houston@xxxxxxxxx
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Corey Minyard wrote:
> 
> I'm trying to get KDB working properly on an SMP machine, and it seems
> to have some problems.  There's KDB_VECTOR, which doesn't seem to be
> tied to anything but seems to be used to stop the other CPUs,
> KDBENTRY_VECTOR, which is for initial entry.  In general, the SMP code
> seems half-done in the patches on the FTP site.
> 
> kdb enters ok and I can debug on the CPU that entered KDB, but I am
> unable to switch to the other CPU and it seems to still be running.
> 
> I read some discussion on the mailing list about this, but there doesn't
> seem to be any resolution.  Is there any?
> 
> Thanks,
> 
> -Corey

Hi Corey,

It sounds like you have a bad merge.  Kdb generally works pretty well
straight out of the bo if you use it with the matching kernel.org 
kernel.  The problem you describe sounds like what I saw mixing
kdb with kgdb stubs.

At least on the x86 the KDB_VECTOR is mostly smoke and mirrors.  The
lowest level of send_IPI functions just sends a broadcast NMI, and the
do_nmi() handler has to guess what caused the interrupt.

There are probably still smp timing issues, but they are more subtle.

Jim Houston - Concurrent Computer Corp.

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