libvirt users - Mar 2014 - Re: how to disable vnet_hdr through libvirt

Thank you Daniel. How difficult to extend libvirt for this? One critical
application on my VM needs to turn vnet_hdr off.
I can switch to use qemu directly. However, in that way I will lose all
the nice things provided by libvirt.

Thanks,
~Jianfeng

On 3/3/14 3:53 AM, "Daniel P. Berrange" <berrange@redhat.com>
wrote:
>On Fri, Feb 28, 2014 at 07:11:13PM +0000, Jianfeng Tang wrote:
>> Hi,
>> 
>> I am using libvirt and virsh to create my VM on KVM. It works fine.
>> However, I need to turn off vnet_hdr for virtio interface.
>> 
>> Does anyone know how to do it through libvirt?
>
>There's no support for disabling it - if we detect a host which supports
>it, it will be unconditionally enabled.
>
>Regards,
>Daniel
>-- 
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On Tue, Mar 04, 2014 at 03:56:06PM +0000, Jianfeng Tang
wrote:
> Thank you Daniel. How difficult to extend libvirt for this? One critical
> application on my VM needs to turn vnet_hdr off.
Can you explain why in more detail. We don't expose this as a configurable
setting because we don't believe there's any compelling reason to
disable
it. ie it offers clear performance benefits with no downsides.

Regards,
Daniel
-- 
|: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org              -o-             http://virt-manager.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org       -o-       http://live.gnome.org/gtk-vnc :|

Daniel P. Berrange <berrange@...> writes:
> 
> On Tue, Mar 04, 2014 at 03:56:06PM +0000, Jianfeng Tang wrote:
> > Thank you Daniel. How difficult to extend libvirt for this? One
critical
> > application on my VM needs to turn vnet_hdr off.
> 
> Can you explain why in more detail. We don't expose this as a
configurable
> setting because we don't believe there's any compelling reason to
disable
> it. ie it offers clear performance benefits with no downsides.
> 
> Regards,
> Daniel

No special reason. Just in my case I was told to turn off vnet_hdr in order
to make my VM work properly. 

I have two choices: extend libvirt or switch to use qemu command.

I asked them to fix it in their product, but it is out of my control and it
did not fit in my timeline.