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SubjectRe: Catching NForce2 lockup with NMI watchdog
On Fri, 12 Dec 2003, Maciej W. Rozycki wrote:

> On Fri, 12 Dec 2003, bill davidsen wrote:
> > | In practice, assuming the MP IRQ routing information provided the BIOS has
> > | been correct (which is not always the case), prerequisites #1 and #2 have
> > | been met so far, but #3 has proved to be occasionally problematic.
> >
> > In practice many system seem to take a good bit of guessing and testing.
> > I have an old P-II which only works with acpi=force and nmi_watchdog=2,
> > for instance.
> Well, the NMI watchdog is a side-effect feature that works by chance
> rather than by design. So you can't really complain it doesn't work
> somewhere, although I wouldn't mind if new hardware was designed such that
> it works. You shouldn't have to use "acpi=force" for the watchdog to work
> though and for a PII system if "nmi_watchdog=1" doesn't work, then I
> suspect a BIOS bug (set APIC_DEBUG to 1 in asm-i386/apic.h and send me the
> bootstrap log and a dump from `mptable' for a diagnosis, if interested).
> > It would be nice if there were a program which could poke at the
> > hardware and suggest options which might work, as in eliminating the
> > ones which can be determined not to work. Absent that trial and error
> > rule, unfortunately.
> Linux has all appropriate bits to set up hardware reasonably as long as
> BIOS provides accurate information. The only case our code fails is when
> BIOS tells us lies and the there's little we can do about it. Actually we
> are doing hardware manufacturers a favor we try to handle some cases at
> all -- it's the BIOS that should be fixed instead and it is software and
> it is stored in Flash memories these days, so there's no excuse. So if
> there's a problem with running Linux because of BIOS bugs, then please
> bugger the manufacturer in the first place (and avoid the company in the
> future if they don't support Linux).
> Sometimes the NMI watchdog works in principle, but its activation leads
> to system instability -- almost always this is a symptom of buggy SMM code
> executed by the BIOS behind our back (NMIs are disabled by default in the
> SMM, but careless code may enable them by accident).

The NMI vector goes to Linux code. In fact all interrupt vectors
go to Linux code. There is no way that some BIOS code could possibly
be accidentally executed here. Some Linux code would have to
call some 16-bit BIOS code somewhere, and it doesn't even know

Dick Johnson
Penguin : Linux version 2.4.22 on an i686 machine (797.90 BogoMips).
Note 96.31% of all statistics are fiction.

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