Re: [Qemu-devel] Bug in recent postcopy patch

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Gary Hook (gary.hook@nimboxx.com) wrote:
> 
> 
> On 10/30/14, 3:08 PM, "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> 
> >>I posted another thread asking about migration failure due to a copy
> >> taking too long, but got no traction. In the case where the problem
> >>raises
> >> its head we have turned tunneling on. A tiny VM (<2GB in size) migrates
> >> fine using the same procedure. Again, no shared storage.
> >
> >Is the guest that doesn't migrate idle or is it busily changing lots of
> >memory?
> 
> Quite idle.  Boot the VM, no need to start a workload, try to migrate.
> Failure.
> 
> Also, very large VMs will fail to migrate (non-tunneled). This _seems_ to
> also be related to the amount of time required to copy everything from A
> to B.
> 
> Again, tunneling seems to more quickly expose this issue as it increases
> the amount of time required to copy the qcow2 file over the network.
> 
> I will add here that I¹ve watched the qcow2 file grow, made a copy of it
> (on the receiving end) before it gets deleted, and been able to start a VM
> using the file. It would seem to be copasetic.
> 
> I need to add tracing code to the emulator, in a way that doesn¹t rely
> upon command line options or environment variables. I don¹t see any such
> facility at this point. Specifically, I want to begin by watching what is
> going through the monitor (I.e. Return values from qemu-system-x86_64 and
> why there are complaints.) Unless you have any clear explanation as to why
> the emulator is throwing an error, could you suggest any areas I may want
> to focus my efforts?

No I don't, but there again I've not done any block stuff, and it sounds like
your problem is mostly related to moving the image file (which I thought
libvirt preferred to do using NBD underneath now, but again, I'm not a block
guy).

> >> >Thanks for the report.
> >> 
> >> Thank you for your time and ownership.
> >
> >No problem; note the postcopy code is still quite young, so don't
> >be too surprised if you hit other issues.
> 
> Of course; it¹s fresh out of the oven. But the migration of VMs using
> non-shared storage is not (tunneled or otherwise), and that¹s really what
> I am focused on.
> 
> Again, much appreciation.

Dave

> Gary
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK