In a recent change Jason Thorpe turned on an option in the USB drivers
that uses soft interrupts.  If a port does not have generic soft interrupts (a
prime example is i386) it instead uses a callout.  In the latter case the
interrupt latency increases greatly.  For most USB devices this has no
consequence, but if you are using, e.g., Ethernet adapters, the performance
will be pretty bad (on my machine it went from 700 KB/s to 140 KB/s).
If this worries you, just change sys/dev/usb/usb_port.h and comment
out the define of USB_USE_SOFTINTR.

    -- Lennart