How to find the slowness on knife vsphere vm vmdk add?

Hello,

I've seen a very annoying slowdown on the knife vsphere vm vmdk add command. Using -VVV I found the slowness: it's on vsphere_vm_vmdk_add.rb between lines 85 and 96.

How can I find who is the real culprit? How I debug this file using my production server?

Thanks.