From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48674) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VEJDT-00008P-RD for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:21:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VEJDN-000514-Ch for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:21:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51362) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VEJDN-00050x-2w for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:21:45 -0400 Date: Tue, 27 Aug 2013 14:21:39 +0100 From: "Richard W.M. Jones" Message-ID: <20130827132139.GA20134@redhat.com> References: <1377187852-11192-1-git-send-email-pbonzini@redhat.com> <87mwo9smjf.fsf@codemonkey.ws> <52164FFD.5030101@redhat.com> <521663A9.6040207@redhat.com> <20130827131334.GT613@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130827131334.GT613@redhat.com> Subject: Re: [Qemu-devel] [libvirt] pvpanic plans? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: pkrempa@redhat.com, marcel.a@redhat.com, libvir-list@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, rhod@redhat.com, Anthony Liguori , Paolo Bonzini , Laszlo Ersek , afaerber@suse.de 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/