Re: Migration problems

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Chris Lalancette wrote:
> All,
>      I've been doing some migration testing of KVM guests, and have been running
> into some problems.  Let me describe the setup and what I've tried, and maybe
> somebody has some ideas about what might be going on here.
>
> Setup:
>      2 identical Intel SDV boxes,  Intel(R) Core(TM)2 Duo CPU     E6850  @ 3.00GHz
>      Both machines are running F-8 kernel, 2.6.23.8-63.fc8 x86_64, with updated
> KVM kernel modules from git.
>      On one machine, I have a /kvm directory that holds my guest disk image;
> this directory is exported via NFS and mounted as /kvm on the secondary machine.
>
> The guest in question is also an F-8 x86_64 guest, running the same kernel as
> the hosts.  I start it up with the following command-line:
>
> qemu-system-x86_64 -hda /kvm/f8x86_64.dsk -boot c -m 385 -net
> nic,vlan=0,macaddr=00:13:6e:12:34:56 -net tap,vlan=0,script=/etc/kvm-ifup
> -monitor stdio
>
> The guest starts up just fine.  On the secondary machine, I use the following
> command-line:
>
> qemu-system-x86_64 -hda /kvm/f8x86_64.dsk -boot c -m 385 -net
> nic,vlan=0,macaddr=00:13:6e:12:34:56 -net tap,vlan=0,script=/etc/kvm-ifup
> -monitor stdio -incoming tcp://0:4444
>
> (i.e. exactly the same, but I add the -incoming parameter).  When I try to do
> live migration this way, things seem like they work, and it even seems like a
> few instructions get executed on the destination side.  However, fairly quickly
> I'll get "Disabling IRQ #11" on the console of the guest at the destination, and
> the qemu process will just spin at 100%, with no interaction possible.  IRQ #11,
> incidentally, is the IRQ associated with the emulated rtl8139 card.
>
> This led me to suspect the in-kernel PIC/APIC emulation, and, sure enough, if I
> pass -no-kvm-irqchip (on both the source and destination), things are better; I
> can at least migrate from the host to the destination without the "Disabling IRQ
> #11" message.  However, if I put any sort of load on the guest while doing
> migration, I still get a hang-up, even with -no-kvm-irqchip.
>
> Has anyone else seen this, or have ideas where I can start debugging it?
>
>   

[copying Uri, who is also chasing migration bugs]

- check the guest kernel without an ioapic
- if that works, check the ioapic load/save paths
- I'd also suspect 3ead9ca0bd2214af63ea2ebf84573576b38e004e or 
71ab66c92f1ecd3f1aabed0bfa2e356fb6bbfebc


-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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