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

[Richard W.M. Jones]

On Tue, Apr 09, 2019 at 06:37:46PM -0700, Sureshkumar Kaliannan wrote:
> 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

I think this is just KVM vs TCG?  You could try enabling nested KVM to
see if that makes things faster, but it very much depends on your host
CPU.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
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