On Tue, Aug 27, 2013 at 8:13 AM, Daniel P. Berrange <berrange@xxxxxxxxxx> 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. Even if you ignore the watchdog aspect of this, having a portable panic notifier and the ability to enhance it to include more information (like the backtrace, etc.) is pretty darn useful. Regards, Anthony Liguori > Daniel > -- > |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| > |: http://libvirt.org -o- http://virt-manager.org :| > |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| > |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list