netdev - Re: Patch for tbench regression.

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Message-ID: <48E10B40.4000205@hp.com>
Date:	Mon, 29 Sep 2008 10:07:12 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	Evgeniy Polyakov <johnpol@....mipt.ru>, netdev@...r.kernel.org,
	Christoph Lameter <cl@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>, David Miller <davem@...emloft.net>,
	Lennert Buytenhek <buytenh@...vell.com>
Subject: Re: Patch for tbench regression.

Sigh - email reading timing....  anyway

> It seems that netperf is issuing 16384-byte writes and as such
> we're sending the packets out immediately so TSO doesn't get a
> chance to merge the data.  Running netperf with -m 65536 makes
> TSO beat non-TSO by 6293Mb/s to 4761Mb/s.

By default, netperf's TCP_STREAM test will use whatever 
getsockopt(SO_SNDBUF) reports just after the data socket is created. 
The choice was completely arbitrary and burried deep in the history of 
netperf.

For evaluating changes, it would probably be a good idea to test a 
number of settings for the test-specific -m option.  Of course I have no 
good idea what those values should be.  There is the tcp_range_script 
(might be a bit dusty today) but those values are again pretty arbitrary.

It would probably be a good idea to include the TCP_RR test.

happy benchmarking,

rick jones

As an asside - I would be interested in hearing peoples' opinions 
(offline) on a future version of netperf possibly violating the 
principle of least surprise and automatically including CPU utilization 
if the code is running on a system which does not require calibration...
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