[libvirt-users] how to setup a watchdog?

hi everybody I'm testing Qemu's watchdog. My understanding was that hardware (here qemu's watchdog) would take action(cold reboot) the system if there is no ping from the OS watchdog, so I thought stopping watchdog service in VM should be a quick test. I have this in the guest: <watchdog model='i6300esb' action='reset'> <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/> </watchdog> and I see /dev/watchdog in my guest. Yet nothing happens. I must be missing something, an expert said it's config problem? many thanks