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SubjectRe: [PATCH] NMI watchdog documentation
On Tue, Jul 29, 2003 at 06:06:30PM +0200, you [Andi Kleen] wrote:
> > Andi, you have the numbers mixed up. mode 1 is I/O-APIC, mode 2 is local APIC,
> > and x86-64 defaults nmi_watchdog to I/O-APIC mode.
> > Now, is it the I/O-APIC or local APIC watchdog that doesn't work in x86-64?
> Right, 1 and 2 need to be exchanged. Anyways local apic mode does not seem
> to work, the kernel always reportss "NMI stuck" at bootup.
> IO APIC mode for is default.
> I have not tested if it works with a 32bit kernel on an Opteron box.

Ok, I'll send the following to Linus and Marcelo unless you object.

-- v --

--- /usr/src/linux/Documentation/nmi_watchdog.txt Mon Jul 28 22:10:18 2003
+++ /usr/src/linux~/Documentation/nmi_watchdog.txt Mon Jul 28 22:18:10 2003
@@ -1,9 +1,11 @@

-Is your ix86 system locking up unpredictably? No keyboard activity, just
+[NMI watchdog is available for x86 and x86-64 architectures]
+Is your system locking up unpredictably? No keyboard activity, just
a frustrating complete hard lockup? Do you want to help us debugging
such lockups? If all yes then this document is definitely for you.

-On Intel and similar ix86 type hardware there is a feature that enables
+On many x86/x86-64 type hardware there is a feature that enables
us to generate 'watchdog NMI interrupts'. (NMI: Non Maskable Interrupt
which get executed even if the system is otherwise locked up hard).
This can be used to debug hard kernel lockups. By executing periodic
@@ -20,6 +22,13 @@
kernel debugging options such as Kernel Stack Meter or Kernel Tracer
may implicitly disable NMI watchdog.]

+For x86-64, the needed APIC is always compiled in, and the NMI watchdog is
+always enabled with perfctr mode. Currently, mode=1 does not work on x86-64.
+Using NMI watchdog (in mode=2) needs the first performance register, so you
+can't use it for other purposes (such as high precision performance
To actually enable the NMI watchdog, use the 'nmi_watchdog=N' boot
parameter. Eg. the relevant lilo.conf entry:

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