Hello,
I'm playing around with KVM for my university and I have some strange
problems with live migration. I hope this is the right place to ask and
maybe somebody can explain why I'm having these problems:
I have a VM running ubuntu and I'm trying to live migrate it. This works
fine if I have just one vcpu for the VM. On the other hand, with 2 vcpus
after the VM migrated to its new host it stops reacting and uses 100% CPU
until killed.
So, first question: Does live migration work with 2 vcpus and just not on
my setup, or is it a bug? Is there anything i can do?
Also, I'm having a performace problem when i try to migrate the VM between
subnets: It takes a very long time before i can use the new ip ( >1.5 sec
inside the VM, which are 8 sec wall clock ).
Basically the diagram below is my setup. The VM is using a bridge to
connect to Host A or B.
+---------- Router -------------- Client
| | 10.0.3.2
| |
| |
Host A Host B
10.0.1.2 10.0.2.2
| |
| (bridged) |
VM <--> VM' `<-->` := live-miration
10.0.1.100 10.0.2.100
When Host A and B are in the same subnet, live migration works great and
downtime of the VM is < 0.4 sec. I've written a daemon, running on the VM,
that recieves messages from the new host and sets a new IP address right
away (no dhcp, just one udp message). The script does something like this
after receiving a message with $NEWIP and $ROUTERIP.
ip addr change $NEWIP dev eth0;
ip route change default via $ROUTERIP;
ping -I $NEWIP $CLIENT # -I explicitly sets the src ip
But this gives a error from ping: There is no device with $NEWIP - I have
to do `sleep 1.5` between the ifconfig and the ping to make this work. To
repeat, the problem is that it takes very long until the new IP is
*usable*, after the time everything works fine.
When i do something similar on a real linux machine i can't find the same
problem. But real machines are much faster, so im not sure if this is a
problem of the VM, or just how linux works. Maybe someone can enlighten me?
thanks in advance,
Jochen
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