From: "Amit S. Kale" <amitkale@emsyssoft.com>
Organization: EmSysSoft
To: Andi Kleen <ak@suse.de>, George Anzinger <george@mvista.com>
Subject: Re: kgdb support in vanilla 2.6.2
Date: Thu, 4 Mar 2004 10:36:58 +0530
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References: <20040204230133.GA8702@elf.ucw.cz.suse.lists.linux.kernel> <40467BC3.7030708@mvista.com> <20040304015056.4d2cc3ee.ak@suse.de>
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On Thursday 04 Mar 2004 6:20 am, Andi Kleen wrote:
> On Wed, 03 Mar 2004 16:43:47 -0800
>
> George Anzinger <george@mvista.com> wrote:
> > Andi Kleen wrote:
> > > On Tue, Mar 02, 2004 at 01:27:51PM -0800, Andrew Morton wrote:
> > >>George Anzinger <george@mvista.com> wrote:
> > >>> Often it is not clear just why we are in the stub, given that
> > >>>we trap such things as kernel page faults, NMI watchdog, BUG macros
> > >>> and such.
> > >>
> > >>Yes, that can be confusing.  A little printk on the console prior to
> > >>entering the debugger would be nice.
> > >
> > > What I did for kdb and panic some time ago was to flash the keyboard
> > > lights. If you use a unique frequency (different from kdb
> > > and from panic) it works quite nicely.

Flashing keyboard lights is far simpler compared to a printk. Printk is too 
heavy. Once a system is unstable, it's more important to run into kgdb code 
asap. Calling printk and co may be too much.

> >
> > Assuming a key board and a clear (no spin locks) path to it.  Still it
> > only says
>
> I think it's reasonable to just write to the keyboard without any locking.
> The keyboard driver will recover.

Flashing keyboard lights is easy on x86 and x86_64 platforms. Is that easy on 
ppc workstations/servers? Embedded boards don't have keyboards.

>
> > we are in kgdb, now why.
>
> The big advantage is that it works even when you are in X (like most
> people) printks are often not visible.

Yep.
-- 
Amit Kale
EmSysSoft (http://www.emsyssoft.com)
KGDB: Linux Kernel Source Level Debugger (http://kgdb.sourceforge.net)

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