[Simh] VMS multinet DHCLIENT/SSH2 configuration problem

[Timothe Litt]

On 28-Jan-18 17:21, Jeremy Begg wrote:
> Hi TIm,
>
>> ...
>> Also I am figuring out how to set SSH2 terminal server. I successfully
>> generated SSH2 keys on emulated SIMH VAX system.
>> ...
>> I installed SIMH and OpenVMS 7.3 on my new Tinker SoC (Pi clone) with
>> Armbian OS for 7/24 operation.
> Once you get SSH working you may find it's unusable.  On my RPi 3 it
> takes the VMS MultiNet SSH server several *minutes* to negotiate the
> SSL handshake.  I suspect (without having attempted any diagnosis!)
> that this is due to SIMH having to emulate a huge number of VAX floating
> point instructions.
I suggest running PCA to determine if this is in fact the cause.  Or
stop the emulation a few times while "hung" and look at the history buffer.

If I had to guess, I'd start by looking at where the required randomness
(for key generation) is coming from.  In most implementations, that's
the cause of typical hangs like these.  I don't know what Multinet is
using for a source of randomness - perhaps Hunter can shed light on that.

FP in SimH isn't that slow - the VAX format is unpacked, then integer
(hardware) operations are performed on the "mantissa" and exponent, then
the result repacked.  These are all integer operations, and should be
reasonably fast on any processor, even a Pi.  The FP code would benefit
from a high level of compiler optimization, as there are lots of
opportunities for inlining.

Note that the PI, and many modern CPUs provide a hardware source of
randomness (which can be behind /dev/{u,}random).  It may be off by
default, depending on your distribution.  I don't think that SimH VAX
uses it, but it might be something to export.  Most older OS would try
to gather randomness from device timing (interrupt jitter), something
that SimH alters...  It can take quite a bit of data to get enough bits
to satisfy randomness (or primality) tests used in key generation.

Anyhow, FP would not be the first place I'd look.

> (Even on my real VAXstation 4000/96 the MultiNet SSH server took up to a
> minute to negotiate the SSL handshake, and of course the system would
> "pause" every now and again while the session keys were renogotiated.
> I had hoped that in moving from a 100MHz VAX to a 1.2GHz SIMH VAX things
> might improve, but they went dramatically backwards.)
>
> Regards
>
>         Jeremy Begg
>
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