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Date:      Sun, 1 Apr 2001 21:54:16 +0200 (CEST)
From:      Bert Driehuis <driehuis@playbeing.org>
To:        "Jason T. Luttgens" <lucky@lansters.com>
Cc:        freebsd-stable@freebsd.org
Subject:   RE: Network performance question
Message-ID:  <Pine.BSI.4.21.0104012144270.4361-100000@c1111.nl.compuware.com>
In-Reply-To: <000001c0bae2$c8c7dad0$0200010a@lucky>

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On Sun, 1 Apr 2001, Jason T. Luttgens wrote:

> One of the things I was using to judge performance was how big of a file the
> tcpdump on the listening machine recorded under each OS (and the number of
> packets reported). But maybe this is not the right way to do this....

Definitely not :-)

> So, what would be a good way to test the performace differences between
> Linux 2.2, 2.4 and FreeBSD as a device to capture 100% packets off the wire
> and not miss any?

Send a predictable load to the device under test (say, include a
sequence number) and use that to determine packet loss (and, also
interesting, packet loss patterns).

You will also have to repeat the test with different cards on each
OS. It is more than conceivable that one OS has better workarounds for
specific ethernet hardware bugs than another, or even that different
trade-offs were made for performance vs reliability.

A case in point is the 3Com 3C905TX, which has a hardware bug that
causes the device to lock up if the receive buffer fills beyond a
certain limit. Limiting the buffer size has an obvious impact on
throughput, but can make the card continue to work where it fails if
left unchecked.

Since vendors keep such hardware bugs under wraps, not all implementors
may even be aware of the bugs, and that can hardly be blamed on them. As
a sideline, I think this policy by the hardware vendors is
counterproductive for them. If they just published the bugs and
workarounds for it (and avoid overhyping their device, so that it still
complies to the minimum specs specs after the workarounds are applied),
I think they'd be better protected against ravenous lawyers than if they
hide the problems until the truth is forced out in court (as in the
floppy controller disaster that cost some vendors huge amounts of
money). Oh well...

Cheers,

			-- Bert

-- 
Bert Driehuis -- driehuis@playbeing.org -- +31-20-3116119
If the only tool you've got is an axe, every problem looks like fun!


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