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-Last reviewed: 06/02/2009
- HP iLO2 NMI Watchdog Driver
- NMI sourcing for iLO2 based ProLiant Servers
- Documentation and Driver by
- Thomas Mingarelli <>
- The HP iLO2 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.
- 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 the Documentation/watchdog/src directory called
- watchdog-test.c. Simply compile the C file and kick it off. If the system
- gets into a bad state and hangs, the HP ProLiant iLO 2 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 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 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 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).
- Below is a list of NMIs the HP BIOS understands along with the associated
- code (reason):
- No source found 00h
- Uncorrectable Memory Error 01h
- PCI Parity Error 20h
- NMI Button Press 27h
- SB_BUS_NMI 28h
- ILO Doorbell NMI 29h
- 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
- (