Re: [PATCH] apci: dump slit

Ingo Molnar
2008-09-14T16:04:35Z

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

> On Sun 2008-09-14 14:26:18, Ingo Molnar wrote:
> >
> > * Pavel Machek <pavel@suse.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@gmail.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