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Date:      Thu, 11 Apr 1996 19:52:17 -0700 (MST)
From:      Terry Lambert <terry@lambert.org>
To:        nathan@netrail.net (Nathan Stratton)
Cc:        freebsd-question@freebsd.org, freebsd-current@freebsd.org
Subject:   Re: What is the max network IO on a FreeBSD box?
Message-ID:  <199604120252.TAA00634@phaeton.artisoft.com>
In-Reply-To: <Pine.LNX.3.92.960411181443.16427B-100000@netrail.net> from "Nathan Stratton" at Apr 11, 96 06:40:56 pm

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> Hi, I am using FreeBSD boxes as routers with Emerging Tech T1 cards. I
> connect them together with 10 Base T, but want to move up to 100 Meg FDDI
> cards. If I put 2 cards in each router, can I shove +100 meg through a P160
> running FreeBSD?
> 
> I am also looking for any T3 cards that FreeBSD supports.

A complying PCI bus runs at 33MHz or less (some people run theirs at
40MHz for 80MHz DX2 machines; these people have problems).

A complying PCI bus is 32 bits (there are some "64 bit" ones, but
they are not yet in the standard and there aren't a bunch of cards).

The maximum burst transfer rate on a 33MHz 32 bit PCI is 132MB/S.

So the bus thinks it can push a couple 100Mbit cards at full bandwidth.
It can burst 8 of them, but you would not be able to maintain that
for any length of time.

The next biggest factor is interrupt processing overhead and external
CPU clock rate (clock multiplied chips are intrinsically I/O binding).

Everything after that tends to be latency, assuming you have a very
fast box.  Latency translates into pool retention time, which for
any given bandwidth translates into memory requirements.

T1 is slow; it shouldn't be a problem.  The best number's I've seen
for FDDI is 60-something  Mbit/S... 2/3's of one wire bandwidth.

You should go over the list archives for the -current list to get the
actual performance figures on the 100 Mbit/S tests (I didn't run them,
I'm just quoting from memory).


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.



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