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Date: Thu, 15 Dec 2005 00:31:06 -0500
From: Jonathan Noack <noackjr@alumni.rice.edu>
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To: Mike Jakubik <mikej@rogers.com>
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Cc: stable@freebsd.org, Mark Kirkwood <markir@paradise.net.nz>
Subject: Re: kernel cpu entries
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Mike Jakubik wrote:
> Mark Kirkwood wrote:
>> Is a minor update to the handbook needed in order avoid confusion 
>> then? e.g. I have been commenting out CPU_I586 on all my PIII systems 
>> in the (mistaken it would seem) belief that having CPU_I686 only was 
>> better.
> 
> Agreed, i have always just used I686, assuming it inherited the features 
> of I586. I think most people will assume this.

A quick benchmark (average of five 'dd' runs sending a large file to 
/dev/null using a blocksize of 32k) similar to that suggested by Matt 
Dillon (http://www.freebsd.org/projects/ideas/#p-memcpy) shows ~3% 
increase with I586_CPU on a dual Pentium III.  This was on a lightly 
loaded live system, but I think it shows that using I586_CPU on an i686 
CPU does show a performance improvement (at least in certain tests).

I have done no testing with blowfish to see how I586_CPU might affect it 
as I use AES, but it seems it should be recommended for i686 CPUs as well.

-Jonathan