Re: [PATCH 0/9][RFC] KVM virtio_net performance

Bill Davidsen
2008-07-27T12:50:08Z

Avi Kivity wrote:
> Bill Davidsen wrote:
>> Anthony Liguori wrote:
>>> Hi Mark,
>>>
>>> [...snip...]

>>> I'm still seeing the same problem I saw with my patch series.
>>> Namely, dhclient fails to get a DHCP address. Rusty noticed that RX
>>> has a lot more packets received then it should so we're suspicious
>>> that we're getting packet corruption.
>>
>> I have been discussing this (on this list) in another thread. Putting
>> tcpdump on the eth0 device in the VM, the br0 device in the host, and
>> the eth0 (physical NIC) in the host, you can see that when the VM
>> generates a DHCP request it shows up on the br0 in the host, but
>> never gets sent on the wire by eth0.
>>
>> That's the point of failure, at least using RHEL5/FC6/kvm-66 as the
>> environment.
>
> Does playing with the bridge forward delay ('brctl setfd') help?
>
Not obviously, default value is 15, stepping from 10..30 made no
difference. It appears the bridge just doesn't forward DHCP packets. I'm
not an expert on bridge setup, and I don't see an obvious control, so I
will look at the code this afternoon and see if something jumps out at me.

--
Bill Davidsen <davidsen@tmr.com>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark