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Last reviewed: 05/20/2016
HPE iLO NMI Watchdog Driver
NMI sourcing for iLO based ProLiant Servers
Documentation and Driver by
The HPE iLO NMI Watchdog driver is a kernel module that provides basic
watchdog functionality and the added benefit of NMI sourcing. Both the
watchdog functionality and the NMI sourcing capability need to be enabled
by the user. Remember that the two modes are not dependent on one another.
A user can have the NMI sourcing without the watchdog timer and vice-versa.
All references to iLO in this document imply it also works on iLO2 and all
Watchdog functionality is enabled like any other common watchdog driver. That
is, an application needs to be started that kicks off the watchdog timer. A
basic application exists in tools/testing/selftests/watchdog/ named
watchdog-test.c. Simply compile the C file and kick it off. If the system
gets into a bad state and hangs, the HPE ProLiant iLO timer register will
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:
soft_margin - allows the user to set the watchdog timer value.
Default value is 30 seconds.
allow_kdump - allows the user to save off a kernel dump image after an NMI.
Default value is 1/ON
nowayout - basic watchdog parameter that does not allow the timer to
be restarted or an impending ASR to be escaped.
Default value is set when compiling the kernel. If it is set
to "Y", then there is no way of disabling the watchdog once
it has been started.
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 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 hpwdt driver can be reloaded.
1. If the kernel has not been booted with nmi_watchdog turned off then
edit and place the nmi_watchdog=0 at the end of the currently booting
kernel line. Depending on your Linux distribution and platform setup:
For non-UEFI systems
For UEFI systems
2. reboot the sever
3. Once the system comes up perform a modprobe -r hpwdt
4. modprobe /lib/modules/`uname -r`/kernel/drivers/watchdog/hpwdt.ko
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 HPE BIOS).
Below is a list of NMIs the HPE BIOS understands along with the associated
No source found 00h
Uncorrectable Memory Error 01h
ASR NMI 1Bh
PCI Parity Error 20h
NMI Button Press 27h
ILO Doorbell NMI 29h
ILO IOP NMI 2Ah
ILO Watchdog NMI 2Bh
Proc Throt NMI 2Ch
Front Side Bus NMI 2Dh
PCI Express Error 2Fh
DMA controller NMI 30h
Hypertransport/CSI Error 31h
-- Tom Mingarelli