Re: Poor performance of ingress filter for separate VMs

[Andy Furniss <adf.lists@gmail.com>]

Neil Aggarwal wrote:
> Hello everyone:
>
> I have a CentOS server running two virtual machines using KVM.
> Each machine has its own virtual device since I am using bridged
> networking.
>
> I am trying to allocate bandwidth to each virtual machine using tc.
>
> I have these rules set up:
>
> /sbin/tc qdisc add dev v1262 ingress handle ffff:
> /sbin/tc filter add dev v1262 parent ffff: protocol ip prio 50 u32 match ip
> src 0.0.0.0/0 police rate 5mbit burst 500k mtu 3100 drop flowid :1
>
> /sbin/tc qdisc add dev v1263 ingress handle ffff:
> /sbin/tc filter add dev v1263 parent ffff: protocol ip prio 50 u32 match ip
> src 0.0.0.0/0 police rate 5mbit burst 500k mtu 3100 drop flowid :1
>
> You can see them when I do a qdisc ls:
>
> qdisc ingress ffff: dev v1262 parent ffff:fff1 ----------------
> qdisc ingress ffff: dev v1263 parent ffff:fff1 ----------------
>
> The problem is when v1262 is doing a large upload, v1263 gets starved.
> If I remove the ingress qdisc, v1263 runs at full speed regardless of what
> v1262 is doing.
> Its as if the two devices are using the same queue.  I did not think that
> would happen since
> they are totally separate devices.
>
> Any ideas what is happening here?

I've never tested with a virtual machine so don't know.

I have suggested mtu 3100 in the past as it happened to work on a quick 
test on a real 100m nic - maybe for vm you need to go higher, or just 
turn off any sort of offload for the virtual device with ethtool and see 
if that helps.

ethtool -k <devname>

to see what the settings are and eg.

ethtool -K <devname> gro off