patch-2.4.22 linux-2.4.22/Documentation/nmi_watchdog.txt

• Lines: 44
• Date: 2003-08-25 04:44:39.000000000 -0700
• Orig file: linux-2.4.21/Documentation/nmi_watchdog.txt
• Orig date: 2001-09-17 23:03:09.000000000 -0700

diff -urN linux-2.4.21/Documentation/nmi_watchdog.txt linux-2.4.22/Documentation/nmi_watchdog.txt
@@ -1,16 +1,38 @@
 
-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
 NMI interrupts, the kernel can monitor whether any CPU has locked up,
-and print out debugging messages if so.  You must enable the NMI
-watchdog at boot time with the 'nmi_watchdog=n' boot parameter.  Eg.
-the relevant lilo.conf entry:
+and print out debugging messages if so.  
+
+In order to use the NMI watchdoc, you need to have APIC support in your
+kernel. For SMP kernels, APIC support gets compiled in automatically. For
+UP, enable either CONFIG_X86_UP_APIC (Processor type and features -> Local
+APIC support on uniprocessors) or CONFIG_X86_UP_IOAPIC (Processor type and
+features -> IO-APIC support on uniprocessors) in your kernel config.
+CONFIG_X86_UP_APIC is for uniprocessor machines without an IO-APIC.
+CONFIG_X86_UP_IOAPIC is for uniprocessor with an IO-APIC. [Note: certain
+kernel debugging options, such as Kernel Stack Meter or Kernel Tracer,
+may implicitly disable the NMI watchdog.]
+
+For x86-64, the needed APIC is always compiled in, and the NMI watchdog is
+always enabled with I/O-APIC mode (nmi_watchdog=1). Currently, local APIC
+mode (nmi_watchdog=2) does not work on x86-64.
+
+Using local APIC (nmi_watchdog=2) needs the first performance register, so
+you can't use it for other purposes (such as high precision performance
+profiling.) However, at least oprofile and the perfctr driver disable the
+local APIC NMI watchdog automatically.
+
+To actually enable the NMI watchdog, use the 'nmi_watchdog=N' boot
+parameter.  Eg. the relevant lilo.conf entry:
 
         append="nmi_watchdog=1"