[Libguestfs] virt-v2v slow when running inside the VM

[Sureshkumar Kaliannan]

Hi,

I'm trying to create a clone of a physical Window VM using p2v.

My goal is to create a cloning tools VM that has libguestfs tools installed
and acts as the convertor.
VM conversion works just fine but the conversion rate is significantly
slow(1/3) when running inside the VM compared to when the v2v is run on the
same bare-metal host.

On the host:
./virt-p2v-20190405-w1f4efxy/virt-v2v-conversion-log.txt:virtual copying
rate: 615.9 M bits/sec
./virt-p2v-20190405-w1f4efxy/virt-v2v-conversion-log.txt:real copying rate:
181.8 M bits/sec

>From the Guest VM (On the same bare-metal host)
virt-p2v-20190405-95azj89j/virt-v2v-conversion-log.txt:virtual copying
rate: 185.1 M bits/sec
virt-p2v-20190405-95azj89j/virt-v2v-conversion-log.txt:real copying rate:
62.7 M bits/sec

I understand there are several factors come into play but i tried to make
the VM comparable by making sure enough CPU / memory is given to the VM.
Also the I played by adjusting the disk cache modes for the VM(cache=none,
cache=unsafe).  When the conversion happens there is not much load and
there are no other VMs on this machine.

I ruled out the disk being the bootleneck because when i do "virt-v2v -i
disk" conversion the VM is only slightly off.
For the same disk image,
virt-v2v when running in the host took '75 sec' whereas in the VM it took
'100 sec'

How to go about debugging this performance issue? Any pointers would be
helpful

thanks
Suresh
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