Re: bad http download speed

Hi Thomas,

I am actually the author of that article. After writing it I posted on
the netbsd-users@ mailing list asking for help.

We've narrowed down the issue: the very low speeds are caused
specifically by the vioif(4) driver. After changing the virtual NIC of
the VM from VirtIO to emulated Intel E1000 (which uses the wm driver),
the speeds ramp up considerably, sometimes beating even Linux and
FreeBSD (although I haven't taken the time to tune those properly yet).
You should check the thread over there for details.

I didn't want to post it here since I wasn't sure if it was a bug, some
missing tunable or network issue, but now I'm pretty sure vioif(4) isn't
able to reach more than 1 MB/s over high latency TCP, no matter how much
I increase the buffer sizes, whereas wm(4) has no trouble. I'm not sure
yet if that should be reported, but I feel like it should.

Now that I get proper speeds with the E1000 NIC, we're troubleshooting
some issues with slow recovery after packet loss, which is a different
(and, as far as I know, known) issue. But things are looking good on
that front.

I'm planning to write a followup article soon to publish the new
findings and rectified measurements. But maybe the vioif performance is
worth looking at.

Thank you,
- z411