I'm not entirely sure my problem is net related.

The problem occurs on 2.0.2/i386 in case it matters.

I wondered why my dump via (ssh tunneled) rmt was so slow (80kB/s).

I boiled it down to having both dump and rmt run on the same machine
(so it can't be the network -- switches or something) and outputting
to /dev/null (so it can't be the tape device). Still only 80kB/s.

Dumping directly to /dev/nrst0 gives close to 2MB/s, so it's not the disk.

I ktraced both ends (dump/ssh and ssh/rmt) and inspected the kdumps
with time stamps.

It looks like, from time to time, the rmt process issues a read call
that only returns after nearly exactly 0.2 seconds for no apparent reason.
Sometimes, this happens while reading large chunks of tape data, but sometimes
it even happens reading a single command character of the rmt protocol.

Any ideas what keeps the rmt process scheduled away for 0.2 seconds?

Thanks.