I'm currently getting great performance from my Quadra 700 running NetBSD
1.4.2 to NAT my 56K PPP connection.  I use the following in the ppp
configuration for dialing and it seems to remove the silo overflow problems
with my US Robotics 56K modem.

cdtrcts
AT&F1&D0

I am currently getting consistent NAT download speeds of 5.0 -6.0 K/s from
the Netscape download window.  I recently tried NetBSD 1.5 with the same
settings and the results were terrible.  Nothing but silo overflows again
and again.

Erik

Halim Chtourou wrote:

> I've read quite a few archived discussions on PPP performance in
> NetBSD/mac68k.  From what I've seen, it seems very hard for the system
> to keep up with any serial connections over 38400. I am using a
> Quadra/Centris 660AV (25mhz '040) with 52MB ram and a SupraExpress 56
> external modem. My NetBSD Mac is only able to reach about half the
> throughput speed (between 2.5k/sec and 3.0k/sec usually) as my G4 with
> internal modem, and even PC with a cheap Motorola winmodem (both can
> reach 4.5-5k/sec and higher).
>
> I am using my NetBSD Centris box as a router with IPNAT for 2 other
> computers on an ethernet network. It is running a 1.4.3 kernel that I
> compiled myself (with unnecessary drivers stripped out and -O3 and
> -m68040 optimizations).  During heavy network activity, even when the
> NetBSD box is idle, I still get many silo overflows:
> Dec 19 14:22:50 littleone /netbsd: zstty0: 14 silo overflows, 0 ibuf
> floods
> Dec 19 14:23:50 littleone /netbsd: zstty0: 9 silo overflows, 0 ibuf
> floods
> Dec 19 14:24:51 littleone /netbsd: zstty0: 13 silo overflows, 0 ibuf
> floods
> Dec 19 14:25:50 littleone /netbsd: zstty0: 4 silo overflows, 0 ibuf
> floods
> Dec 19 14:27:44 littleone /netbsd: zstty0: 9 silo overflows, 0 ibuf
> floods
> Never had an ibuf flood though.
> Those results are when the system is idle, I have gotten over 100 silo
> overflows in a minute during heavy system activity.
>
> I have tried various port speeds, including 57600, 115200, and even
> 230400, all with similar results. (although overflows seem to occur most
> at 230400). I have also tried both cdtrcts and crtscts flow control
> options. Is this problem simply due to a lack of support for Serial DMA
> in NetBSD/mac68k? If so, can we ever expect to see this added in the
> (near?) future?
>
> I have also tried various modem init strings, including disabling modem
> compression and setting the S26 register (RTS->CTS delay time), with no
> luck.
>
> I would love to be able to use my NetBSD system for this, but unless I
> can find a solution to this speed problem, I have to just put it out in
> the shed to collect dust...
>
> -Halim Chtourou