path: root/Documentation/watchdog/hpwdt.txt
diff options
authorTom Mingarelli <>2009-06-18 23:28:57 +0000
committerWim Van Sebroeck <>2009-06-23 07:13:45 +0000
commit44df75353bc8f32e26e049284053a61d4f1047d6 (patch)
tree8ac01af7888c6d5c3746d30834fd63a148305078 /Documentation/watchdog/hpwdt.txt
parent789cd4702bf830416d2e1794495407be42fe95ad (diff)
[WATCHDOG] hpwdt: Add NMI priority option
Add a priority option so that the user can choose if we do the NMI first or last. Signed-off-by: Thomas Mingarelli <> Signed-off-by: Wim Van Sebroeck <>
Diffstat (limited to 'Documentation/watchdog/hpwdt.txt')
1 files changed, 15 insertions, 4 deletions
diff --git a/Documentation/watchdog/hpwdt.txt b/Documentation/watchdog/hpwdt.txt
index 127839e53043..9c24d5ffbb06 100644
--- a/Documentation/watchdog/hpwdt.txt
+++ b/Documentation/watchdog/hpwdt.txt
@@ -19,30 +19,41 @@ Last reviewed: 06/02/2009
not be updated in a timely fashion and a hardware system reset (also known as
an Automatic Server Recovery (ASR)) event will occur.
- The hpwdt driver also has three (3) module parameters. They are the following:
+ The hpwdt driver also has four (4) module parameters. They are the following:
soft_margin - allows the user to set the watchdog timer value
allow_kdump - allows the user to save off a kernel dump image after an NMI
nowayout - basic watchdog parameter that does not allow the timer to
be restarted or an impending ASR to be escaped.
+ priority - determines whether or not the hpwdt driver is first on the
+ die_notify list to handle NMIs or last. The default value
+ for this module parameter is 0 or LAST. If the user wants to
+ enable NMI sourcing then reload the hpwdt driver with
+ priority=1 (and boot with nmi_watchdog=0).
NOTE: More information about watchdog drivers in general, including the ioctl
interface to /dev/watchdog can be found in
Documentation/watchdog/watchdog-api.txt and Documentation/IPMI.txt.
- The NMI sourcing capability is disabled when the driver discovers that the
- nmi_watchdog is turned on (nmi_watchdog = 1). This is due to the inability to
+ The priority parameter was introduced due to other kernel software that relied
+ on handling NMIs (like oprofile). Keeping hpwdt's priority at 0 (or LAST)
+ enables the users of NMIs for non critical events to be work as expected.
+ The NMI sourcing capability is disabled by default due to the inability to
distinguish between "NMI Watchdog Ticks" and "HW generated NMI events" in the
Linux kernel. What this means is that the hpwdt nmi handler code is called
each time the NMI signal fires off. This could amount to several thousands of
NMIs in a matter of seconds. If a user sees the Linux kernel's "dazed and
confused" message in the logs or if the system gets into a hung state, then
- the user should reboot with nmi_watchdog=0.
+ the hpwdt driver can be reloaded with the "priority" module parameter set
+ (priority=1).
1. If the kernel has not been booted with nmi_watchdog turned off then
edit /boot/grub/menu.lst and place the nmi_watchdog=0 at the end of the
currently booting kernel line.
2. reboot the sever
+ 3. Once the system comes up perform a rmmod hpwdt
+ 4. insmod /lib/modules/`uname -r`/kernel/drivers/char/watchdog/hpwdt.ko priority=1
Now, the hpwdt can successfully receive and source the NMI and provide a log
message that details the reason for the NMI (as determined by the HP BIOS).