VirtualBox, Windows Guest Virtual Machines, and The VirtIO Network Interface

Despite how long I have been running Windows in virtual machines (as far back as Vmware Workstation 1.0), I have never gotten around to looking at the virtio network interface – except for naïvely turning it on once, finding it didn’t work, and turning it off – so I decided to have a look at it. I was prompted to do this by a suggestion that emulating the NIC hardware as opposed to simply using a virtual communications channel to the host would hurt network performance. Good job I chose a long weekend because I ran into a few issues :-

• Getting appropriate test tools took a while because most of the tools I know of are very old; I ended up using iperf2 on both the Linux main host and the Windows 10 guest (within the “Windows
• The “stable” virtio drivers (also called “NetKVM”) drivers didn’t work. Specifically they could send packets but not receive them (judging from the DORA conversation that was more of a DODO). I installed the “latest” drivers from https://fedoraproject.org/wiki/Windows_Virtio_Drivers. Note to late readers: this was as of 2017-04-30; different versions may offer different results.
• Upgrading my ancient Debian Jessie kernel to 4.9 on the off-chance it was a kernel bug turned into a bit of an exercise what with ZFS disappearing after the upgrade, and sorting out the package dependencies to get it re-installed was “interesting” (for small values of course). No data loss though.

I ran two tests :-

1. sudo nping –tcp -p 445 –count 200 –data-len 1280 ${ip of windows guest) – to judge how reliable the network connection was.
2. On the Linux host: sudo iperf -p 50001 
3. On the Windows guest (from within the Ubuntu-based environment): sudo iperf -p 50001 -c ${ip of Linux host}

Which is not the result I was expecting. And yes I did repeat the tests a number of times (I’ve cheated and chosen the best numbers for the above table), and no I did not confuse which NIC was configured at the time of the tests nor did I get the tests mixed up. And to those who claim that the use of the Ubuntu environment screwed things up, that appears not to be the case – I repeated the test with a Windows compiled version of iperf with much the same results.

So it seems despite common sense indicating that a NIC “hardware” custom designed for a virtual environment should perform better than an emulation of a hardware NIC, the actual result in this case was the other way around. Except for the nping result which shows the loss of a single packet with the emulated hardware NIC.