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x86, nmi-watchdog: update procfs nmi_watchdog file documentation v2

Impact: improve documentation

This patch updates the /proc/sys/kernel/nmi_watchdog documentation.
Updated: included Randy Dunlap's corrections.

Signed-off-by: Aristeu Rozanski <>
Acked-by: Randy Dunlap <>
Signed-off-by: Ingo Molnar <>
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1 parent b062f84 commit 8a1c8eb75be492e20003966652c9cd5ff57a559d Aristeu Rozanski committed with Ingo Molnar Oct 30, 2008
Showing with 11 additions and 3 deletions.
  1. +6 −3 Documentation/filesystems/proc.txt
  2. +5 −0 Documentation/nmi_watchdog.txt
@@ -1338,10 +1338,13 @@ nmi_watchdog
Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero
the NMI watchdog is enabled and will continuously test all online cpus to
-determine whether or not they are still functioning properly.
+determine whether or not they are still functioning properly. Currently,
+passing "nmi_watchdog=" parameter at boot time is required for this function
+to work.
-Because the NMI watchdog shares registers with oprofile, by disabling the NMI
-watchdog, oprofile may have more registers to utilize.
+If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel parameter), the
+NMI watchdog shares registers with oprofile. By disabling the NMI watchdog,
+oprofile may have more registers to utilize.
@@ -69,6 +69,11 @@ to the overall system performance.
On x86 nmi_watchdog is disabled by default so you have to enable it with
a boot time parameter.
+It's possible to disable the NMI watchdog in run-time by writing "0" to
+/proc/sys/kernel/nmi_watchdog. Writing "1" to the same file will re-enable
+the NMI watchdog. Notice that you still need to use "nmi_watchdog=" parameter
+at boot time.
NOTE: In kernels prior to 2.4.2-ac18 the NMI-oopser is enabled unconditionally
on x86 SMP boxes.

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