From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47735) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VEJ8v-00038P-1I for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:17:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VEJ8r-0003ZV-7O for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:17:08 -0400 Received: from mail-ob0-f170.google.com ([209.85.214.170]:59093) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VEJ8r-0003YC-3N for qemu-devel@nongnu.org; Tue, 27 Aug 2013 09:17:05 -0400 Received: by mail-ob0-f170.google.com with SMTP id eh20so4715692obb.1 for ; Tue, 27 Aug 2013 06:17:01 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <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> <20130827131334.GT613@redhat.com> Date: Tue, 27 Aug 2013 08:17:00 -0500 Message-ID: From: Anthony Liguori Content-Type: text/plain; charset=ISO-8859-1 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, "Michael S. Tsirkin" , libvir-list@redhat.com, marcel.a@redhat.com, qemu-devel , rhod@redhat.com, Paolo Bonzini , Laszlo Ersek , =?ISO-8859-1?Q?Andreas_F=E4rber?= On Tue, Aug 27, 2013 at 8:13 AM, 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. 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 :|