ppp halting problems on sparc

Richard Henderson (richard@atheist.tamu.edu)
Tue, 3 Sep 1996 20:25:23 -0500 (CDT)

Well, with any of the several patches posted a couple of days
ago PPP functions on the Sparc Voyager.

It is not, however, pleasant.

Everything is very jerky. E.g. "cat /usr/dict/words" puts two
or three second pauses between the packets. FTP is nightmarish,
degenerating to full minute pauses within a few KB (I have a
tcpdump trace of this). This can be repeated at will with any
of Linux, Sunos, Solaris or A/UX as the peer.

The problem does not appear to be in the serial code itself, because
when connected directly through the modem, the data streams down
just fine. (This was a doubt of mine because the 2.0.10 I got from
Red Hat had a halting problem just connecting through the modem.
2.0.16 seems to have cleared this up.)

Looking carefully, I actually see the same problem on my Alpha,
although to a lesser extent. That is, the "burst frequency"
appears to be higher; enough so that telnet is usable, though
cat /usr/dict/words makes the problem more visible. If one
considers that the timer interrupt frequency is ~10 times higher
on the Alpha, this might point to the problem.

Not really knowing how ppp and the serial port communicate, could
there be a delay problem there? Where, exactly, might I go to look?

This line of thinking might also be nothing -- the smoothness on
the Alpha when connected directly might be just that the bytes are
delivered to the console in ones and twos rather than entire packets.


If anyone has any ideas or needs info, please ask. I have limited
direct access to the machine, so results might not be terribly
prompt, but I'll do my best.