linux-kernel - Re: [PATCH] apci: dump slit

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Message-ID: <20080914155928.GB4845@ucw.cz>
Date:	Sun, 14 Sep 2008 17:59:29 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] apci: dump slit

On Sun 2008-09-14 14:26:18, Ingo Molnar wrote:
> 
> * Pavel Machek <pavel@...e.cz> wrote:
> 
> > On Fri 2008-09-12 23:19:21, Thomas Gleixner wrote:
> > > On Fri, 12 Sep 2008, Andi Kleen wrote:
> > > > "Yinghai Lu" <yhlu.kernel@...il.com> writes:
> > > > >
> > > > > to see how wrong could be set by BIOS.
> > > > 
> > > > Just dump it from user space then.  There are plenty of tools
> > > > to access ACPI tables.
> > > 
> > > 1.) what guarantees that we reach user space ?
> > 
> > We can dump in *any* kernel.
> >
> > > 2) If it is _valuable_ information which we can gather via kernel
> > >    output, then it is much more conveniant than asking the user to type
> > >    whatevercryptictoolcommandline and provide the output.
> > 
> > Ooh, 'lets dump more junk at everyone, typing commands is hard' :-(.
> 
> no, the principle is, information like the boot-time CPUID information 
> (and even the BIOS environment) can be indicative of _kernel bugs_. It 
> is often essential to dump what the booting (and failing) kernel thinks 
> is its environment.
> 
> Often that environment is corrupted (by the kernel) and that leads to 
> problems. This 'environment' can also be affected by things like hard 
> boot vs cold boot differences, whether it's in a kexec environment, 
> whether it's booted as a virtual guest, etc., etc.
> 
> For a long time we had the kernel's x86 bootup pretty much as a mostly 
> silent black box and when it broke we tried to figure things out 
> afterwards which was difficult and error-prone. Now we've got various 
> quite effective debug mechanisms (which includes printouts as well) and 
> figuring out x86 problems is visibly easier. We definitely wont go back 
> to the 'black box code, can only be debugged by a few experts' method.
> 
> So extending on that is a good and obvious idea in general - and i agree 
> with Peter that this should be command-line dependent, i.e. not printed 
> by default. Only printing it when 'debug' is specified on the command 
> line is a good solution.

Dumping when user requested it on commandline seems like good
compromise to me.
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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