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

[Sureshkumar Kaliannan]

thanks Richard,

The experiment was indeed done with nested VM enabled. I am not sure about
the internals, but i thought once overlay is setup the 2 main processes are
sshd and qemu-img convert (reading data from sshd and doing the conversion)
I don't see any of the qemu process running.
Initial overlay setup was pretty quick and rest of the time was spent in
qemu-img convert operation

Suresh

On Wed, Apr 10, 2019 at 6:22 AM Richard W.M. Jones <rjones at redhat.com>
wrote:

> 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,
> bindings from many languages.  http://libguestfs.org
>
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