On 06/17/2009 11:12 AM, Fischer, Anna wrote:
For the tests I run now (with vlan= enabled) I am actually using both TCP and UDP, and I see the problem with virtio_net for both protocols. What I am wondering about though is that I do not seem to have any problems if I communicate directly between the two guests (if I plug then into the same bridge and put them onto the same networks), so why do I only see the problem of stalling network communication when there is a routing VM in the network path? Is this just because the system is even more overloaded in that case? Or could this be an issue related to a dual NIC configuration or the fact that I run multiple bridges on the same physical machine?
My guess is that somewhere there's a queue that's shorter that the
virtio queue, or its usable size fluctuates (because it is shared with
something else). So TCP flow control doesn't work, and UDP doesn't have
a chance.
When you say "We are working on fixing this." - which code parts are you working on? Is this in the QEMU network I/O processing code or is this virtio_net related?
tap. virtio, qemu, maybe more. It's a difficult problem.
Retry with "the fixed configuration"? You mean setting the vlan= parameter? I have already used the vlan= parameter for the latest tests, and so the CPU utilization issues I am talking about are happening with that configuration.
Yeah.
Can you compare total data sent and received as seen by the guests?
That would confirm that packets being dropped causes the slowdown.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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