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Date:      Mon, 02 Apr 2001 16:15:23 -0700
From:      Mike Smith <msmith@freebsd.org>
To:        "Jason T. Luttgens" <lucky@lansters.com>
Cc:        "'Doug Hardie'" <bc979@lafn.org>, freebsd-stable@FreeBSD.ORG, "'David W. Chapman Jr.'" <dwcjr@inethouston.net>
Subject:   Re: Network performance question 
Message-ID:  <200104022315.f32NFO702856@mass.dis.org>
In-Reply-To: Your message of "Mon, 02 Apr 2001 19:08:14 EDT." <000001c0bbc9$cc97b990$0200010a@lucky> 

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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).

It's a reasonable assumption; it sounds like you haven't tuned the 
FreeBSD box very well, so it's doing a lot of disk I/O.

> 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).

This sounds like the NetGear card has issues with other PCI bus activity.

> 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?

Looks like you have PCI-domain issues.  Possibly you need to tweak the 
latency timer, it's also possible that your disk controller is 
misbehaving (you don't say what you're using, so it's hard to guess 
here).  You probably want to talk to Bill Paul and see if the NetGear 
card needs crutches to deal with busy busses.

Regards,
Mike
-- 
... every activity meets with opposition, everyone who acts has his
rivals and unfortunately opponents also.  But not because people want
to be opponents, rather because the tasks and relationships force
people to take different points of view.  [Dr. Fritz Todt]
           V I C T O R Y   N O T   V E N G E A N C E



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