5.x, 6.x and CPUTYPE

Craig Boston craig at feniz.gank.org
Mon Nov 7 19:23:31 PST 2005


On Tue, Nov 08, 2005 at 12:05:13PM +1000, Joel Hatton wrote:
> Thanks, Craig. I'm glad to hear that I'm not alone in pursuing this method.
> Do you know of any particular disadvantages of continuing with this
> less-than-optimised model - I guess I mean, is this something that is
> likely to break or become uneconomical at some point?

It won't break; after all the release binaries are targeted for 386 (or
maybe 486 now) in order to be able to run on anything.  You might need
to update make.conf with the "pentiumpro" name just in case they ever
drop the i686 alias, but that's about it.

You might not get quite as good performance as if you compiled for
exactly your CPU (keep in mind we're probably talking about 1-2% at most
unless you have a VERY specific workload that SSE could benefit), but
IMO it's more than worth it to be able to plug the hard drives into a
similar machine and have things Just Work.

Personally, I pick i686 (pentiumpro) as a good middle ground.  The
features optimized for by that are present in every modern
x86-architecture CPU: P2, P3, P4, Athlon, etc.  So it's unlikely you'll
run into something older than that.  Also, the ppro has most of the
features that really affect performance -- i.e. the gap between 386/486
and 686 is a lot bigger than the gap between 686 and P3/P4.

P3s/P-M and Athlons especially are fairly smart and will optimize a lot
of things at runtime.  P4s are probably where you'll see the biggest
performance hit -- that's where Intel tried to push a lot off it off on
the compiler.

Craig


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