From: Pawel Krawczyk [anti_kravietz@ceti.pl]
Sent: Wednesday, July 04, 2001 1:16 PM
To: Info-VAX@Mvb.Saic.Com
Subject: Re: DECnet performance with Linux

LBohan@dbc.spam_less..com wrote:

> does the performance drop at 200KB, happen in both directions 
> (to/from ...).. 

I have only tested Linux->VAX direction

> and to clarify, at some size above 200KB,  the copy speed 
> degrades so badly,  the copy fails all together ?

After 200 KB something was going, but one packet every 10 seconds. I'm not
sure if it was data, tcpdump identified it as some link control packets,
different from the data that was going before.

I've already got reply from DECnet/Linux maintainer, Patrick
Caulfield.  He instructed me to change one Linux kernel variable, namely
NSP_MAX_WINDOW from default 2046 to 1 and this helped. Those of you who
know DECnet will probably know exactly what was the problem.

Just for summary, the fix for 2.4 Linux kernels is to edit
/usr/src/linux/include/net/dn.h and change

#define NSP_MAX_WINDOW	(0x07fe)

 to:

#define NSP_MAX_WINDOW	(1)

And recompile kernel/modules.

-- 
Paweł Krawczyk *** home: <http://ceti.pl/~kravietz/>
security: <http://ipsec.pl/>  *** fidonet: 2:486/23