Schroedinger's VM

[Jerry James]

I'm still a virtualization in Fedora newbie, so forgive me if this is
a stupid question.  Today I started a kernel compile going in a
qemu-kvm virtual machine on one desktop, switched to another desktop,
then left for lunch.  When I got back, I switched back to the original
desktop to see how the compile had gone.  It was still going.  I ran
top, which showed a short-term load of over 4 and a long-term load of
near zero, along with 3 cc1 processes near the top of the list.  As I
sat there puzzling over what had happened, the compile finished.
Other compiles have finished in only a few minutes.  That near-zero
load makes me suspect that the VM simply stopped doing anything while
I was gone.

I've done a couple of more tests now and have seen the same thing.  I
can start a download going, switch to another desktop, wait for
awhile, then switch back.  The download has progressed only a short
amount past when I switched away from that desktop, and (apparently)
abruptly resumes when I switch back to the desktop containing the VM
window.

Is this expected?  Do KVM-based VMs have to be looked at to do
anything?  If so, is there an option somewhere along the lines of
RunEvenWhenIAmNotLookingAtYou=true?

[Richard W.M. Jones]

On Tue, Apr 21, 2009 at 03:23:46PM -0600, Jerry James wrote:
> I've done a couple of more tests now and have seen the same thing.  I
> can start a download going, switch to another desktop, wait for
> awhile, then switch back.  The download has progressed only a short
> amount past when I switched away from that desktop, and (apparently)
> abruptly resumes when I switch back to the desktop containing the VM
> window.
>
> Is this expected?  Do KVM-based VMs have to be looked at to do
> anything?  If so, is there an option somewhere along the lines of
> RunEvenWhenIAmNotLookingAtYou=true?

Can you use virt-top (or even plain top) to look at the qemu-kvm
process.  Is it doing anything when you are switched to the other
desktop?

Rich.

[Jerry James]

On Tue, Apr 21, 2009 at 3:50 PM, Richard W.M. Jones  wrote:
> Can you use virt-top (or even plain top) to look at the qemu-kvm
> process.  Is it doing anything when you are switched to the other
> desktop?
>
> Rich.
>
> --
> Richard Jones, Emerging Technologies, Red Hat  http://et.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://et.redhat.com/~rjones/virt-df/

I've waited for over half an hour now on the other desktop, and
qemu-kvm is sitll consuming 15% to 20% of the real CPU, just like it
was when I first switched away.  Hmmmm....  I'm using this virtual
machine to do some experimental Linux kernel work.  It's got nothing
whatsoever to do with scheduling, but now I wonder if I broke or
misconfigured something.

Let's assume the problem is due to me mucking about in the kernel
unless I uncover evidence to the contrary.  Thanks, Rich.

[Mark McLoughlin]

On Tue, 2009-04-21 at 15:23 -0600, Jerry James wrote:
> Is this expected?  Do KVM-based VMs have to be looked at to do
> anything?

Short answer, yes.

Longer answer, yes in some circumstances, but it's a bug.

Another answer, not if you use libvirt and virt-viewer :-)

When using the SDL backend (i.e. instead of qemu-kvm -vnc), if you
switch workspaces using Ctrl-Alt-Arrow, then SDL tries to grab the
pointer and fails and keeps retrying until you switch back to the
workspace.

Fully gory details, here:

https://bugzilla.redhat.com/480065

What's preventing this from being fixed is the patch getting upstream.

We don't recommend people use the SDL backend, really. The VNC backend
is far better tested.

Cheers,
Mark.

[Jerry James]

On Wed, Apr 22, 2009 at 1:07 AM, Mark McLoughlin  wrote:
> Short answer, yes.
>
> Longer answer, yes in some circumstances, but it's a bug.
>
> Another answer, not if you use libvirt and virt-viewer :-)
>
> When using the SDL backend (i.e. instead of qemu-kvm -vnc), if you
> switch workspaces using Ctrl-Alt-Arrow, then SDL tries to grab the
> pointer and fails and keeps retrying until you switch back to the
> workspace.
>
> Fully gory details, here:
>
> https://bugzilla.redhat.com/480065
>
> What's preventing this from being fixed is the patch getting upstream.
>
> We don't recommend people use the SDL backend, really. The VNC backend
> is far better tested.
>
> Cheers,
> Mark.

Thanks, Mark.  That is very helpful information.

Let me tell you, F-11 can't come out soon enough.  I'm becoming more
and more tempted to install the preview release next week, which I've
never done before, just so I can take advantage of the shiny new virt
stuff.  Then I can revert back to virt-manager without having to
suffer through the tiny window size that made me stop using it on
F-10.

[Bill Davidsen]

Jerry James wrote:
> I'm still a virtualization in Fedora newbie, so forgive me if this is
> a stupid question.  Today I started a kernel compile going in a
> qemu-kvm virtual machine on one desktop, switched to another desktop,
> then left for lunch.  When I got back, I switched back to the original
> desktop to see how the compile had gone.  It was still going.  I ran
> top, which showed a short-term load of over 4 and a long-term load of
> near zero, along with 3 cc1 processes near the top of the list.  As I
> sat there puzzling over what had happened, the compile finished.
> Other compiles have finished in only a few minutes.  That near-zero
> load makes me suspect that the VM simply stopped doing anything while
> I was gone.
>
> I've done a couple of more tests now and have seen the same thing.  I
> can start a download going, switch to another desktop, wait for
> awhile, then switch back.  The download has progressed only a short
> amount past when I switched away from that desktop, and (apparently)
> abruptly resumes when I switch back to the desktop containing the VM
> window.
>
> Is this expected?  Do KVM-based VMs have to be looked at to do
> anything?  If so, is there an option somewhere along the lines of
> RunEvenWhenIAmNotLookingAtYou=true?

KVM using SDL doesn't have any issues I've ever found running unwatched. 
I run a bunch of servers that way, starting in tiny windows and parked 
on an unwatched desktop. Only if I need to look at something do I go there.

[Jerry James]

Hi Bill,

On Fri, Apr 24, 2009 at 10:14 AM, Bill Davidsen  wrote:
> KVM using SDL doesn't have any issues I've ever found running unwatched. I
> run a bunch of servers that way, starting in tiny windows and parked on an
> unwatched desktop. Only if I need to look at something do I go there.

Have you seen Mark McLoughlin's reply in this thread?  If not, look here:

https://bugzilla.redhat.com/480065

Regards,