|Last reviewed: 06/02/2009
|HP iLO2 NMI Watchdog Driver
|NMI sourcing for iLO2 based ProLiant Servers
|Documentation and Driver by
|Thomas Mingarelli <firstname.lastname@example.org>
|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
|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
|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