[rhelv6-list] KVM causing interface overruns

[Jack Neely]

Folks,

I had some network performance problems on one of my KVM VMs recently.
Switching to the virtio network driver made the VM usable.  However, in
this process I noticed that the VM host machine has a high number of
overruns for the vnetX interfaces attached to each VM.  Especially so
for UDP-heavy processes such as PXE booting (TFTP).

vnet0     Link encap:Ethernet  HWaddr FE:52:00:01:01:94  
          inet6 addr: fe80::fc52:ff:fe01:194/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1352052 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13098674 errors:0 dropped:0 overruns:1527 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:140258512 (133.7 MiB)  TX bytes:959158287 (914.7 MiB)

I've seen the overruns much higher before I switched to the virtio
network driver.  What is causing the overruns?  They seem to severely
impact network performance.

My KVM hosts are RHEL 6.2 using the latest kernel and updates.

Jack Neely
-- 
Jack Neely <jjneely at ncsu.edu>
Linux Czar, OIT Campus Linux Services
Office of Information Technology, NC State University
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