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

  • To: Xen User-List <xen-users@xxxxxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: Virajith Jalaparti <virajith.j@xxxxxxxxx>
  • Date: Tue, 11 Jan 2011 20:51:23 -0600
  • Cc:
  • Delivery-date: Tue, 11 Jan 2011 18:52:42 -0800
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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.


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