Re: [libvirt] [Qemu-devel] pvpanic plans?

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.