umass(4)/uhci(4) REALLY slow

[Nate Lawson]

Here are "iostat 5" results for my USB thumb drive on a uhci(4) controller
with 5.1-CURRENT.  On windows on the same box, it runs reasonably quickly.
On FreeBSD, it really lags.  This is for a cp of a large file to a
msdosfs-mounted flash drive.

     da0
  KB/t tps  MB/s
  1.07  41  0.04
  1.00  41  0.04
  1.02  41  0.04

Is there something we're doing on uhci(4) that makes each transfer only
1 KB?  If we upped it to 32 KB, it would be a more reasonable 1.2 MB/sec
which is still well under the USB 1.1 max speed.

Thanks,
-Nate