From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46633) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VEJ5b-00012B-R3 for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:13:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VEJ5Y-0002Xq-0x for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:13:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62975) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VEJ5X-0002Xe-PB for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:13:39 -0400 Date: Tue, 27 Aug 2013 14:13:34 +0100 From: "Daniel P. Berrange" Message-ID: <20130827131334.GT613@redhat.com> References: <1377187852-11192-1-git-send-email-pbonzini@redhat.com> <87mwo9smjf.fsf@codemonkey.ws> <52164FFD.5030101@redhat.com> <521663A9.6040207@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <521663A9.6040207@redhat.com> Subject: Re: [Qemu-devel] [libvirt] pvpanic plans? Reply-To: "Daniel P. Berrange" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: pkrempa@redhat.com, mst@redhat.com, libvir-list@redhat.com, marcel.a@redhat.com, qemu-devel@nongnu.org, rhod@redhat.com, Anthony Liguori , Laszlo Ersek , afaerber@suse.de 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. 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 :|