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From: cak@purdue.UUCP (Christopher A. Kent)
Newsgroups: net.lan
Subject: Re: Problems with IP/UDP speed on Vax750/Unix4.2
Message-ID: <485@mordred.purdue.UUCP>
Date: Tue, 11-Feb-86 09:45:26 EST
Article-I.D.: mordred.485
Posted: Tue Feb 11 09:45:26 1986
Date-Received: Wed, 12-Feb-86 21:36:24 EST
References: <776@duvan.UUCP>
Organization: Department of Computer Science, Purdue University
Lines: 36
Summary: How to make it faster..

In article <776@duvan.UUCP>, ahi@duvan.UUCP (Anders Hillbo) writes:
> We want to connect a VAX 750, running UNIX BSD 4.2, with an Interlan
> controller and a custom made display station (Intel iSBC 186/51 & 82586
> based) to transfer image data. We decided to use Ethernet and an UDP/IP 
> implementation on the displaystation to be able to run in user mode on the
> Vax.
> 
> The problem is SPEED (on the 750).
> 
> The display station is just now capable of sending data in up to 300 kbyte/s.
> the VAX computer only send data in 33 kbyte/s
> 
> Also when sending TO the Vax the interface or something seems to drop packets
> if 4 of them arrive immediatly after each other. (I thought Interlan
> could handle back-to-back packets).
> 
> The goal is a transfer rate at about 100 kbyte/s.

I expect that the main problem is the VAX's i/o system; it can't handle the 
interrupt load quickly enough. The Interlan card can handle back-to-back
packets, but on a limited basis; it has some internal buffer space,
but it's not infinite.

I'd go for bigger packets. There's no reason not to use full ethernet
packets (1500 bytes), but you'll probably have to hack the VAX's kernel. I'm
afraid I've only done this for the TCP layer, so I can't give you exact
directions.

We never used trailers here, because we have some binary-only equipt
that doesn't understand them. I believe that the VAX only does
trailers on those sizes because that's when it uses "tear-away"
pages for buffers; tuning your packet sizes to use trailers and pages
will also help a lot (the mbuf mechanism has a lot of overhead.

Good luck,
chris