CPUTYPE in general - was Re: Which CPUTYPE for a dualcore Xeon on AMD64

[Stephen Montgomery-Smith]

Jack L. wrote:
> On 6/24/07, Martin Turgeon <martin at optiksecurite.com> wrote:
>> Hi,
>>
>> I recently installed AMD64 6.2 Release on 2 PowerEdge servers, both with
>> dual core Xeon (3070 and 5110). I noticed when I was updating the
>> sources that it was compiling as an Athlonxp by default. I was wondering
>> if I should change the CPUTYPE in make.conf to something else. I read at
>> some places that it is not recommended because it could cause problems
>> but I thought it would be interesting to start the debate here. Please
>> note that I would prefer not to go with the -STABLE or -CURRENT branch
>> because these a going to be essential productions servers.
>>
>> Thank you for your opinions,
>>
>> Martin
> I use nocona. That should be the correct one.

I know I am hijacking the thread a bit - but:

In general, how does one decide which CPUTYPE to use?  The connection 
between the options for CPUTYPE and the output of dmesg is not so 
obvious to me.  I looked at the features advertised by dmesg (which in 
my case included SSE3) and then reverse engineered bsd.cpu.mk to figure 
out I should be using "prescott," but I am hoping I figured it out the 
hard way.

Also, does setting CPUTYPE make a lot of difference to performance?  
Right now I have no CPUTYPE set at all.

Thanks, Stephen