Re: [Bugme-new] [Bug 7495] New: Kernel periodically hangs.

[Arjan van de Ven <arjan@infradead.org>]

On Sun, 2006-11-12 at 14:37 +0100, Adrian Bunk wrote:
> On Sun, Nov 12, 2006 at 02:16:16PM +0100, Arjan van de Ven wrote:
> > 
> > > Some APIC-related bugs in the kernel Bugzilla that have been reported or 
> > > confirmed during the last 12 months (I only looked at "apic" in the 
> > > subject, there might be more related bugs in the Bugzilla):
> > > 
> > > #5038 Fast running system clock with IO-APIC enabled
> > 
> > This is a UP machine. NotInteresting(tm) wrt APIC.
> >... 
> 
> Currently it's a supported configuration.

define "supported"; we have code to try it and it's great if it works.
But if it doesn't... you're out of luck.

We KNOW it can't work on a sizable amount of machines.  This is why it
is a config option; you can enable it if YOUR machine is KNOWN to work,
and you get some gains. But it's also understood that it often it won't
work. So any sensible distro (since they have to aim for a wide
audience) disables this option ...

> 
> We must either handle such cases or explicitely disable the APIC on all 
> UP machines 

that'd be the same as setting the config option off...
> > I think that's a mistake. But oh well, I suspect in practice ACPI/BIOS
> > cause it to be turned off automatic most of the time.
> 
> I'd doubt the latter. Even on my cheap Asus board running an i386
> AMD Athlon XP with 1.8 GHz the APIC is both used and working without any
> problems.

"it works on my one machine so it works for everyone". That's simply not
true. We KNOW it can't work everywhere on UP, especially on i386. SMM
assumptions; people gluing the apic pins to the reset line, we've seen
it all. 
That it works for you is great. But that doesn't mean it automatically
works for everyone.



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