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Date:      Mon, 2 Apr 2001 19:08:14 -0400
From:      "Jason T. Luttgens" <lucky@lansters.com>
To:        "'Doug Hardie'" <bc979@lafn.org>, <freebsd-stable@FreeBSD.ORG>
Cc:        "'Mike Smith'" <msmith@FreeBSD.ORG>, "'David W. Chapman Jr.'" <dwcjr@inethouston.net>
Subject:   RE: Network performance question
Message-ID:  <000001c0bbc9$cc97b990$0200010a@lucky>
In-Reply-To: <f0433011db6edd7194143@[10.0.1.3]>

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Ok, I've done some re-testing on the suggestions of a few people. I created
a known data set of 500000 packets with a data value in each packet that
increments by one. This way I can tell what packets are lost, if any.

Interestingly enough, the Linux 2.4.3 kernel captured almost all packets.
FreeBSD 4.2 and 3.5.1 were off by 1000+.

However - I noticed something while testing. Linux 2.4.3 did not access the
drive as much as FreeBSD was. I guess Linux is caching the file more or
something...who knows. So I re-performed the tests with output going to
/dev/null and looking at the tcpdump and interface counters (I know, it's
not the best way, but at this point I was thinking it's the disk I/O that's
causing the drops/loss).

I tried the test under FreeBSD with the NetGear card too - in addition to
the 3COM. It's kinda strange, but when using the NetGear card and outputting
tcpdump to /dev/null there were no problems, not even many interface errors
(where as writing to a file causes the network to go down and tons of
interface errors about halfway through the capture).

When outputting tcpdump to /dev/null, performance was comparable +- 5
packets each time between Linux 2.4.3 and FreeBSD. Sometimes FreeBSD got a
couple more, sometimes Linux 2.4.3 did.

It would seem I need to perform a sustained load test...like spew packets
for a day and then compare. Maybe that's what I'll do next.

Anyone know what might be going on here?


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