pppd performance / silo overflow

[Thomas Ribbrock <emgaron_(_at_)_gmx_(_dot_)_net>]

Hi all,

I just went through the archive to find an explanation for the "silo
overflow" message(s) I get, and the majority seems to think that a few of
them are nothing to worry about. Fair enough. I'm just wondering, how few
are "few"? Reason I'm asking is that I have problems with the modem
performance on my machine. It's a 486DX4-100 (OpenBSD 2.6) with four cards
in it: Graphics card (VLB), Multi I/O- and HD controller card (HD is on VLB,
rest is on ISA, all I/O ports are disabled with jumpers), additional I/O
card with parallel/serial port on ISA (serial ports have 16550a FIFOs) and a
3c509b NIC on ISA (PnP is disabled, irq 5, addr 0x360). The ISA bus is
currently overclocked (CLKIN/3 instead of CLKIN/4 - that's 11MHz, if I
understand it correctly) as that brought a slight improvement with the
problem below. To the best of my knowledge, there are no interrupt conflicts
(all that's found according to dmesg is on different irqs).

The modem is a 56k one, so I had pppd set up to try 115200baud on the serial
port first (which I had succesfully used on similar hardware, albeit with
another OS). I got a "few" silo overflow messages, usually stating 5-8
overflows. The performance of the PPP link was ok at first and then suddenly
deteriorated catastrophically to just a couple of 100 bytes/s, loads of
drop-outs - but no more "overflow" messages, strangely enough. Will those
messages always be displayed whenever there is an overflow? (Or, the other
way round: If I don't get them, can I safely assume there are no overflows?)

I then set pppd to use 57600baud instead. The performance was a *lot* better
and basically what I would expect. I still get silo overflows, though, but
not very often and only "1"s.

The machine runs IP Filter as firewall and for masquerading and performs
POP3 downloads every now and then - but that's all that's going on. The
heaviest load would be some Real Audio streaming or downloads.

Does anybody happen to have an idea whether I should expect to be able to
run the serial port at "full tilt" (=115200) on this setup? Or is 57600
indeed as good as it gets? I know it won't make a hell of a difference - I'm
more curious as to whether there could be something I've done wrong (I'm
still learning - but OpenBSD sure seems worthwhile learning!).

Thanks in advance,

Thomas
-- 
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      Thomas Ribbrock    http://www.bigfoot.com/~kaytan    ICQ#: 15839919
   "You have to live on the edge of reality - to make your dreams come true!"