[Xen-devel] Live migration-delay in gratuitous arp

[Virajith Jalaparti <virajith.j@xxxxxxxxx>]

Hi,

I was trying to perform live migration with a VM on a LAN and measure 
the downtime seen by an application (e.g. ping), the time for which the 
application cannot communicate with the VM. The application is run on a 
machine different from those between which the VM is migrated. I noticed 
that the VM remains unreachable for nearly 1-1.5sec. However the 
xend.log file says that the time (the delta) for the last round of the 
migration is around 100msec. So, the VM is actually paused for just 
around 100msec but the application cannot reach it for 1-1.5sec. I 
believe this is because of the delay in the gratuitous ARP being sent. 
Is the implementation such that the ARP is not sent immediately after 
the migration is finished? Is there an easy tweak (without modifying 
source code) by which I can correct this or do I have to modify the 
source code?
I am using Xen from the repos of CentOS 5.5 on a 64bit machine.

Thanks,
Virajith



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