9600+ baud performance on 4.0

[Dave Pare]

I've just started reading this newsgroup recently, so this may be old hat
to the rest of you folks.

We just converted our fileserver from 3.5 to 4.0.1.  We have a 3/260 with
an mti (16-port multiplexor) board, along with a few Telebit Trailblazer
Plus modems.  As soon as we converted, inbound uucp transfers from our
news and uucp server started to time out for files larger than about 8k.
No file above about 50k would transfer at all.

Turns out that the 4.0.1 streams implementation is not a great performer
when things happen at 9600 baud or better.  Telebits in
fast/compressed/uucp mode can get up to 16000 baud -- at least that's the
fastest I've observed.  It appears that the streams implementation starts
dropping characters at that rate, which greatly confuses the telebits
which after a while simply refuse to talk with the uucico process.  Uucico
eventually times out.

Outbound uucp traffic works just fine.

The fix?  Well, we ran over to sun and they were kind enough to give us a
4.0.3 kernel, which we dropped into place.  If you run telebits on your
sun, and you want 4.0, you NEED 4.0.3.  If things aren't working well for
you now, then that may be why.

Even under 4.0.3 I've noticed some problems, however.  Timeouts still
occur, and by watching the "vmstat" I observe that the system still can't
get the data quite fast enough to satisfy those speedy telebits.  I don't
know what implications this "streams" implementation has for other serial
devices (like the X terminal we just got from Graph-On), but I bet it
doesn't bode well if they speak faster than 9600 baud.

One problem could be that the system appears to interrupt for each
character generated by uucico.  I've seen 1200 interrupts per second on
the modem lines during uucico transfers.  Doesn't this seem odd?  Is this
the way things used to behave under 3.5?

Dave