netdev - Re: tcp bw in 2.6

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Message-ID: <20071002154137.GD17418@bitmover.com>
Date:	Tue, 2 Oct 2007 08:41:37 -0700
From:	lm@...mover.com (Larry McVoy)
To:	lm@...mover.com, Herbert Xu <herbert@...dor.apana.org.au>,
	torvalds@...ux-foundation.org, davem@...emloft.net,
	wscott@...mover.com, netdev@...r.kernel.org
Subject: Re: tcp bw in 2.6

Interesting data point.  My test case is like this:

server
	bind
	listen
	while (newsock = accept...)
		transfer()

client
	connect
	transfer

If the server side is the source of the data, i.e, it's transfer is a 
write loop, then I get the bad behaviour.  If I switch them so the data
flows in the other direction, then it works, I go from about 14K pkt/sec
to 43K pkt/sec.

Can anyone else reproduce this?  I can extract the test case from lmbench
so it is standalone but I suspect that any test case will do it.  I'll
try with the one that John sent.  Yup, s/read/write/ and s/write/read/
in his two files at the appropriate places and I get exactly the same
behaviour.

So is this a bug or intentional?
-- 
---
Larry McVoy                lm at bitmover.com           http://www.bitkeeper.com
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