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Re: [Qemu-devel] [libvirt] pvpanic plans?
From: |
Richard W.M. Jones |
Subject: |
Re: [Qemu-devel] [libvirt] pvpanic plans? |
Date: |
Tue, 27 Aug 2013 14:21:39 +0100 |
User-agent: |
Mutt/1.5.20 (2009-12-10) |
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
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- Re: [Qemu-devel] pvpanic plans?, (continued)
- Re: [Qemu-devel] pvpanic plans?, Peter Maydell, 2013/08/22
- Re: [Qemu-devel] pvpanic plans?, Richard W.M. Jones, 2013/08/27
- Re: [Qemu-devel] pvpanic plans?, Ronen Hod, 2013/08/27
- Re: [Qemu-devel] pvpanic plans?, Richard W.M. Jones, 2013/08/27
- Re: [Qemu-devel] pvpanic plans?, Anthony Liguori, 2013/08/27
- Re: [Qemu-devel] [libvirt] pvpanic plans?, Daniel P. Berrange, 2013/08/27
- Re: [Qemu-devel] [libvirt] pvpanic plans?, Anthony Liguori, 2013/08/27
- Re: [Qemu-devel] [libvirt] pvpanic plans?,
Richard W.M. Jones <=
Re: [Qemu-devel] pvpanic plans?, Laszlo Ersek, 2013/08/22