On Tue, Aug 27, 2013 at 02:13:34PM +0100, Daniel P. Berrange wrote: > On Thu, Aug 22, 2013 at 09:16:57PM +0200, Paolo Bonzini wrote: > > Il 22/08/2013 19:53, Laszlo Ersek ha scritto: > > >> > We should just introduce a simple watchdog device based on virtio and > > >> > call it a day. Then it's cross platform, solves the guest enumeration > > >> > problem, and libvirt can detect the presence of the new device. > > > If the guest doesn't initialize the proposed virtio-panic device, then > > > it will lie dormant too, just like the current pvpanic device. That's good. > > > > > > However a new (standalone) virtio device will take up yet another PCI > > > function (a full device if you want it to be hotpluggable). PCI > > > functions are scarcer than ioports. > > > > Not just that. Panic notifiers are called in a substantially unknown > > environment, with locks taken or interrupts already set up. > > > > This is why we went for a simple ISA device. Configuration via ACPI > > follows naturally from there, and anyway any other standard of the day > > would have had the same problem with Windows. At some point we had ACPI > > methods instead of a simple ioport write, but we had to remove that > > because the ACPI subsystem might have had its lock taken. > > > > Also, a virtio watchdog device makes little sense, IMHO. PV makes sense > > if emulation has insufficient performance, excessive CPU usage, or > > excessive complexity. We already have both an ISA and a PCI watchdog, > > and they serve their purpose wonderfully. > > I also don't think that panic notifiers & watchdogs are really > serving the same purpose. The panic notifier is an alert to a > specific known kernel crash. A watchdog is merely a timeout, > which is inferred to mean /something/ went wrong. Both have > their uses IMHO & we should not conflate the two. Exactly this. They are two different things. Of course ILOs combine both (and more) in one mega-device :-) Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/ -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list