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

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Message-ID: <20080914160403.GA20082@elte.hu>
Date:	Sun, 14 Sep 2008 18:04:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Pavel Machek <pavel@...e.cz>
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


* Pavel Machek <pavel@...e.cz> wrote:

> 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.

great! Yinghai, mind reworking the patch in that direction please? I'd 
suggest to enable the optional dumping of all things BIOS environment 
related, not just the ACPI/SLIT.

there's also CONFIG_X86_VERBOSE_BOOTUP=y [default disabled] - which 
could be coupled with an x86=verbose boot parameter or so.

	Ingo
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