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Re: fix TCP roundtrip time update code

To: Nivedita Singhvi <niv@xxxxxxxxxx>
Subject: Re: fix TCP roundtrip time update code
From: David Mosberger <davidm@xxxxxxxxxxxxxxxxx>
Date: Tue, 3 Jun 2003 22:34:30 -0700
Cc: davidm@xxxxxxxxxx, "David S. Miller" <davem@xxxxxxxxxx>, kuznet@xxxxxxxxxxxxx, jmorris@xxxxxxxxxxxxxxxx, gandalf@xxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxx, netdev@xxxxxxxxxxx, akpm@xxxxxxxxx
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>>>>> On Tue, 03 Jun 2003 21:40:18 -0700, Nivedita Singhvi <niv@xxxxxxxxxx> 
>>>>> said:

  Nivedita> David Mosberger wrote:
  DaveM> So if your old SpecWEB99 lab tended more to trigger timeout
  DaveM> based retransmits on LAN, and your new test network does not,
  DaveM> then your new test network will tend to not reproduce the bug
  DaveM> regardless of whether the bug is present in the kernel or not
  DaveM> :-)

  >>  Is this where I get to plug httperf?  It triggered the bug
  >> reliably in less than 10 secs. ;-)

  Nivedita> Tarnation!! Ran httperf! Didnt hit it! :(. What were your
  Nivedita> settings?

I used:

 $ httperf --rate 1000 --num-conns 1000000 --verbose --hog --server HOST \
        --uri pathto30KBfile

on 3 clients (for a total of 3000 conns/sec).  You can't go higher
than 1000 conn/sec per client (IP address) because otherwise you run
out of port space (due to TIME_WAIT).

This load worked well for a machine with a single GigE card.  All
network tunables were on the default setting (in particular, the tx
queue len was 300, which is were the losses came from).

With this load, I saw bad RTT values in the route cache within a
couple of seconds after starting the third httperf generator.  It then
took a bit longer (on the order of 1-2 minutes) until the first
TCPAbortFailed errors started to pop up.

        --david

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