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Re: [Qemu-devel] pvpanic plans?

From: Richard W.M. Jones
Subject: Re: [Qemu-devel] pvpanic plans?
Date: Tue, 27 Aug 2013 09:06:57 +0100
User-agent: Mutt/1.5.20 (2009-12-10)

On Thu, Aug 22, 2013 at 03:09:06PM -0500, Anthony Liguori wrote:
> Paolo Bonzini <address@hidden> writes:
> > 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.
> Neither of which actually work with modern versions of Windows FWIW.

Correct, although someone could write a driver!

> Plus emulated watchdogs do not take into account steal time or
> overcommit in general.  I've seen multiple cases where a naive watchdog
> has a problem in the field when the system is under heavy load.

The watchdog devices in qemu run on guest time.  However the watchdog
*daemon* inside the guest probably does behave badly as you describe.
Changing the device model isn't going to help this, but it would
definitely make sense to fix the daemon (although I don't know how --
is steal time exposed to guests?)

I don't necessarily think a virtio-watchdog is a bad idea.  For one
thing it'd mean we would have a watchdog device that works on ARM.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.

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