libvirt users - Jun 2017 - [qemu-kvm] Network bandwidth limits via libvirt

Hi all,

I try to understand why the network bandwidth limits are not applied to my
ubuntu 16.04.2 VM (qemu-kvm driver) and I would need some insights.
I create my VM network with virsh and when I issue a dumpxml on my network, I
can see that bandwidth limits are set:

virsh # net-dumpxml nat_limit
<network>
  <name>nat_limit</name>
  <uuid>4b5e128d-9ad0-4ccc-9424-dee60b71861a</uuid>
  <forward mode='nat'>
    <nat>
      <port start='1024' end='65535'/>
    </nat>
  </forward>
  <bridge name='virbr1' stp='on' delay='0'/>
  <mac address='52:54:00:af:99:73'/>
  <bandwidth>
    <inbound average='10' peak='50' burst='10'/>
    <outbound average='128' peak='256'
burst='256'/>
  </bandwidth>
  <ip address='192.168.123.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.123.2' end='192.168.123.254'/>
    </dhcp>
  </ip>

</network>


And the net info is:
virsh # net-info nat_limit
Name:           nat_limit
UUID:           4b5e128d-9ad0-4ccc-9424-dee60b71861a
Active:         yes
Persistent:     yes
Autostart:      yes
Bridge:         virbr1
Then, I create my VM, and the source of interface is the network, like this:
virsh # dumpxml virt20
...
    <interface type='network'>
      <mac address='52:54:00:a2:5b:10'/>
      <source network='nat_limit' bridge='virbr1'/>
      <target dev='vnet2'/>
      <model type='rtl8139'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00'
slot='0x03' function='0x0'/>
    </interface>
...


However when I send a big file with netper I don't see any limits applied to
the transfer rate.

I've checked the domain log and I didn't see any qemu command line
argument related to bandwidth limits.


Could you tell me why the network bandwidth limits can not work? Do network
limits are managed in another way?
Thanks.

Below some information about my hypervisor:

root@ubuntu-04:~# virsh -V
Virsh command line tool of libvirt 1.3.1
See web site at http://libvirt.org/

Compiled with support for:
 Hypervisors: QEMU/KVM LXC UML Xen LibXL OpenVZ VMWare VirtualBox ESX Test
 Networking: Remote Network Bridging Interface netcf Nwfilter VirtualPort
 Storage: Dir Disk Filesystem SCSI Multipath iSCSI LVM RBD Sheepdog ZFS
 Miscellaneous: Daemon Nodedev AppArmor Secrets Debug Readline Modular

qemu version: 2.5.0

Thanks,

Netsurfed

On 06/15/2017 07:56 AM, 卓浩凡 wrote:
> Hi all,
> 
> I try to understand why the network bandwidth limits are not applied to my
ubuntu 16.04.2 VM (qemu-kvm driver) and I would need some insights.
> I create my VM network with virsh and when I issue a dumpxml on my network,
I can see that bandwidth limits are set:
> 
> virsh # net-dumpxml nat_limit
> <network>
>   <name>nat_limit</name>
>   <uuid>4b5e128d-9ad0-4ccc-9424-dee60b71861a</uuid>
>   <forward mode='nat'>
>     <nat>
>       <port start='1024' end='65535'/>
>     </nat>
>   </forward>
>   <bridge name='virbr1' stp='on' delay='0'/>
>   <mac address='52:54:00:af:99:73'/>
>   <bandwidth>
>     <inbound average='10' peak='50'
burst='10'/>
>     <outbound average='128' peak='256'
burst='256'/>
>   </bandwidth>
>   <ip address='192.168.123.1'
netmask='255.255.255.0'>
>     <dhcp>
>       <range start='192.168.123.2'
end='192.168.123.254'/>
>     </dhcp>
>   </ip>
> 
> </network>
Have you restarted network after editing?
virsh net-destroy nat_limit && virsh net-start nat_limit;
> 
> 
> And the net info is:
> virsh # net-info nat_limit
> Name:           nat_limit
> UUID:           4b5e128d-9ad0-4ccc-9424-dee60b71861a
> Active:         yes
> Persistent:     yes
> Autostart:      yes
> Bridge:         virbr1
> Then, I create my VM, and the source of interface is the network, like
this:
> virsh # dumpxml virt20
> ...
>     <interface type='network'>
>       <mac address='52:54:00:a2:5b:10'/>
>       <source network='nat_limit' bridge='virbr1'/>
>       <target dev='vnet2'/>
>       <model type='rtl8139'/>
>       <alias name='net0'/>
>       <address type='pci' domain='0x0000'
bus='0x00' slot='0x03' function='0x0'/>
>     </interface>
> ...
> 
> 
> However when I send a big file with netper I don't see any limits
applied to the transfer rate.
Where are you sending the file from? If it is the host then the limits
should be applied. If it is from another virtual machine, then
unfortunately limits are set, but since kernel takes some shortcuts and
the packets don't travel through bridge but are copied from one vNIC to
another one. In that case you might want to use <bandwidth/> for your
<interface/> directly.

The golden rule here is follow the packets. In case of network, the
limiting is applied on the bridge, so packets must go through bridge in
order for limits to apply. In case of <interface/> the limits are
applied there.

Michal