Subject: Re: [PATCH] myr10ge: again fix lro_gen_skb() alignment

From: Rick Jones <[email-masked]>
Date: Fri, 24 Apr 2009 10:13:52 -0700

> This is strange.  I wonder if it might be a cache footprint issue?
> My intentionally weak receiver is an athlon64 x2 "Toledo", and
> has only 512KB L2 cache.  I can re-test with a core-2 based Xeon.

A point about netperf :)  By default, it will use one more buffer than the 
initial size of the socket buffer divided by the send/recv buffer size - this 
goes back to days of copy-avoidance, a flavor of which can be found in reading:

ftp://ftp.cup.hp.com/dist/networking/briefs/copyavoid.pdf

particularly section 3.2.  It can be overridden with the global -W option:

     -W send,recv      Set the number of send,recv buffers

Of course, this will interact with other things such as:

The default send/recv size will be the send/recv socket buffer size. That can be 
overridden with the test-specific -m/-M options.

The default socket buffer size will be whatever the system gives it.  That can be 
overridden with the test-specific -s/-S options.

So, the various options can have a non-trivial effect on the cache footprint of 
the data netperf is shoving around.

rick jones