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Re: Slow network performance with KVM



Katynski, Bogdan wrote:
> > Bob Proulx wrote:
> > What is the output:
> > 
> >   $ lsmod | grep vhost_net
> 
> I don't have the module loaded and what's worse - I don't have this module :(
> 
> root@vmhost:~# modprobe vhost-net
> FATAL: Module vhost_net not found.
> ...
> I don't have these options In my kvm processes. Do I need an
> additional package with this module? Or maybe a backported more
> recent kernel?

I forgot that this module is only available in later kernels!  Sorry.
It does not appear in Squeeze.  It does exist in 2.6.39 because I did
find it there.  Here is data from a Sid machine that routinely gets
updated and has a lot of history.

  $ locate vhost_net.ko
  /lib/modules/2.6.39-2-amd64/kernel/drivers/vhost/vhost_net.ko
  /lib/modules/3.0.0-2-amd64/kernel/drivers/vhost/vhost_net.ko
  /lib/modules/3.1.0-1-amd64/kernel/drivers/vhost/vhost_net.ko
  /lib/modules/3.2.0-1-amd64/kernel/drivers/vhost/vhost_net.ko
  /lib/modules/3.2.0-2-amd64/kernel/drivers/vhost/vhost_net.ko
  /lib/modules/3.2.0-3-amd64/kernel/drivers/vhost/vhost_net.ko
  /lib/modules/3.2.0-4-amd64/kernel/drivers/vhost/vhost_net.ko

On Squeeze you would want to use a backported 3.2 kernel.  It would be
worthwhile to try it if you are suffering from this performance
problem.  Here are instructions:

  http://backports-master.debian.org/Instructions/

I recently described the procedure in some detail here:

  https://lists.debian.org/debian-user/2012/12/msg00351.html

You might also want to try the backported newer versions of
libvirt-bin kvm packages.  There have been several improvements.
However the internal PCI device numbering did change and this will
prevent some VMs from starting due to conflicts until their xml
configuration file has been updated.  Either update the xml or
recreate the VM.  If you hit this problem I can clue you in as to the
xml edit to make.  It is simple but I forget off the top of my head at
this moment.

Bob

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