Re: 3.0.4 and 3.1-rc4 based dom0 won't boot with acpi=off

[Ian Campbell <Ian.Campbell@citrix.com>]

On Sat, 2011-09-10 at 20:44 -0400, Sven Köhler wrote:
> Am 11.09.2011 02:28, schrieb Konrad Rzeszutek Wilk:
> > On Sun, Sep 11, 2011 at 12:43:18AM +0200, Sven Köhler wrote:
> >> Hi,
> >>
> >> when using acpi=off in the kernel or xen command line, the system won't
> >> boot. On real hardware, I saw a few interrupt related warnings from the
> >> usb drivers. The system then seemed to lock up when trying to do I/O via
> >> AHCI. Same in virtualbox. System won't come up.
> > 
> > Not surprised. Without the ACPI we can't find parse the interrupt table,
> > so you don't get any interrupts.
> 
> Thanks for explaining. Now what about the future? Will there be some
> solution for the acpi=off case?
> 
> I'm a bit confused, since your words don't sound like there is a way to
> boot with acpi=off. But other dom0 kernels actually boot with acpi=off.
> So after all, some other way for setting up interrupts seems to exist.

Using acpi=off is sometimes a useful way to diagnose an issue, and once
upon a time it may have even done more good than harm and been a useful
solution to get a machine to work (on native as well under Xen) but on a
modern system disabling ACPI is likely to do more harm than good, it's
simply too ingrained into the way things work these days (again, on
native as much as under Xen).

> So in fact, xen is doing the reboot, and not the dom0 kernel, right?
> (Some people have claimed otherwise)

The dom0 kernel reboot method is always "via Xen", which is probably
where the confusion arises, in many cases dom0 _initiates_ the reboot
but doesn't actually do the reboot itself, Xen does the actual rebooting
since it is the only entity with access to the required mechanisms in
most cases.

> Could you imagine to adapt xen's reboot code to the one of linux 3.0
> (which was tweaked quite a lot for maximum compatibility)

It's probably worth revisiting and resyncing with what Linux does, IIRC
Matthew Garret did a bunch of work on this recently. In particular 
        
        commit 660e34cebf0a11d54f2d5dd8838607452355f321
        Author: Matthew Garrett <mjg@redhat.com>
        Date:   Mon Apr 4 13:55:05 2011 -0400
        
            x86: Reorder reboot method preferences
            
but also all the stuff in the quirks file I suppose.

Ian.

> 
> 
> Regards,
>   Sven
>