[libvirt-users] Need to increase the rx and tx buffer size of my interface

[Michal Privoznik]

On 10/25/2017 01:53 PM, Ashish Kurian wrote:
> Dear Users/Developers,
> 
> I am using a KVM Ubuntu VM as a degrader to apply specific delays to
> incoming packets. As the delay for my packets can be higher than 7.5
> seconds, there is not enough buffer on my interface to buffer all the
> packets. Therefore those overflowing packets are dropped in the machine and
> not forwarded.
> 
> When I tried to use the command  ethtool -G ens8 rx 512 to increase the
> buffer size, I get the following error.
> 
> Cannot set device ring parameters: Operation not permitted
> 
> I have kept the VM xml files as specified in the link :
> https://libvirt.org/formatdomain.html. The value that I kept in my xml file
> is as follows.
> 
> <interface type='direct'>
>       <mac address='52:54:00:72:f9:eb'/>
>       <source dev='enp7s0f0' mode='vepa'/>
>       <model type='virtio'/>
>       <driver name='vhost' queues='5' rx_queue_size='512'
> tx_queue_size='512'>
>       <host csum='off' gso='off' tso4='off' tso6='off' ecn='off' ufo='off'
> mrg_rxbuf='off'/>
>       <guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off'/>
>       </driver>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x08'
> function='0x0'/>
>     </interface>
>     <interface type='direct'>
>       <mac address='52:54:00:00:b5:99'/>
>       <source dev='enp7s0f1' mode='vepa'/>
>       <model type='virtio'/>
>       <driver name='vhost' queues='5' rx_queue_size='512'
> tx_queue_size='512'>
>       <host csum='off' gso='off' tso4='off' tso6='off' ecn='off' ufo='off'
> mrg_rxbuf='off'/>
>       <guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off'/>
>       </driver>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x09'
> function='0x0'/>

So what does the qemu command line look like? You can find it in either
libvirtd log or domain log.

http://wiki.libvirt.org/page/DebugLogs

Michal