🚀 go-pugleaf

I've found the problem.

The i486 box has two (ISA) bus masters: an Adaptec 1542CF SCSI
host adapter, and the AT1500 ethernet card.

The SCSI host adapter was set to 6.7 MHz DMA rate, and has been
for almost 3 years without a problem.

However, this seems to upset the ethernet card. When the SCSI
host adapter DMA rate is reduced to 5.7 MHz, the ftp
throughput jumps to between 900 and 1000 Kbyte/s (ftp'ing a 19
MByte file to /dev/null). The exact figure depends on whether
the operation is a get or a put, and which host is the server.

Interestingly, "get" transfers to /dev/null under samba, using
smbclient on the i486 box, also run at 1000 Kbyte/s (transferring
the same 19 MByte file).

There were some clues to the problem, but, being new to
ethernets, I didn't realise they were important.
On the i486 box:

    - ifconfig was reporting Rx errors for eth0;

    - /var/log/messages was reporting a very occasional
      error message, but only when eth0 was *idle*:
        eth0: Bus master arbitration failure, status 88f2

Thanks to everyone who emailed or posted their comments: these
put me on the right track.

Alan