[HECnet] Emulated XQ polling timer setting and data overrun

[Johnny Billquist]

On 2014-06-05 17:55, Mark Pizzolato - Info Comm wrote:
On Thursday, June 05, 2014 at 5:59 AM, Johnny Billquist wrote:
On 2014-06-05 13:58, Mark Pizzolato - Info Comm wrote:
On Thursday, June 05, 2014 at 1:27 AM, Johnny Billquist wrote:
On 2014-06-05 02:38, Jean-Yves Bernier wrote:
    [...]
I have tested commit 753e4dc9 on Mac OS 10.6, no virtualization.
Both simh instances run on the same hardware. XQ set to different
MAC addresses, since this is now enforced.

Asynchronous network/disk IO may explain the uncommon transfer
speed
(I
have filled a   RM03 in seconds).

Interesting. I still have real network issues with the latest simh
talking to a real PDP-11 sitting on the same physical network. So you
seem to have hit sime other kind of limitation or something...

Can you elaborate on these 'real network issues'?

This is the first I've heard of anything like this.

I have not had any experience with a real PDP11 talking to a simh PDP or
VAX, but in the past there were no issues with multiple simh VAX simulators
talking to real VAX systems on the same LAN.

Let me know.

Same as I have talked about several times here. Doing file transfers from the
simh system to the real PDP-11 gets horrible performance. It's a simple
question of data overflow and loss, and DECnet performs poorly here
because recovery from lost packets is so bad when you are loosing lots of
packets.

Nothing you really can do about it, unless you want to throttle the ethernet
transmissions.

Hmmm...

There are several possibilities which may help or otherwise be relevant:

1) Your real PDP11 is connected to the LAN via some sort of transceiver.   Hopefully you're not using Thickwire or Thinwire Ethernet, but some sort of 10BaseT transceiver connected to a switch port.   I've seen switch ports which are VERY POOR at auto-detecting link speed and duplex (especially when dealing with 10Mbit devices).   If you're connected through a managed switch, try to hard set the switch port's link speed to 10Mbit and Half Duplex.
2) Try to extend the number of receive buffers available using CFE as you mentioned.

Hopefully one of these will help.

It don't. Believe me, I've seen this, and investigated it years ago.
When you have a real PDP-11 running on half-duplex 10Mb/s talking to something on a 1GB/s full duplex, the PDP-11 simply can't keep up.

This is (repeating myself once more) why I implemented the throttling in the bridge. Talking to the PDP-11 with the bridge sitting inbetween it works just fine.

Traffic also works fine if the fast machine isn't trying to totally drown the PDP-11. So things like interactive traffic, and small stuff works just fine. File transfers is the obvious problem child.

	Johnny