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Note Pentium Optimized only really helps P5 CPUs ...

On Fri, Jul 02, 1999 at 05:51:39AM -0500, R. Brock Lynn wrote:
> I'd be impressed, as I'm sure a lot of other folks would to at a
> decision from Debian to add to it's list of offerings, a pentium
> optimized set of packages.

[NB: this is just a pre-emptive strike before a thousand people jump into
this thinking that "Pentium optimizations" will speed up their machine a
lot.  I'm just pointing out the architectural restrictions that make the
Pentium a machine for which optimized code makes a huge difference.  If
this bores you, delete this now and feel no remorse.]

I don't want to throw water on this fire, since the ability to layer
things architecturally would be a great benefit to Debian.  But before
everyone does the Stampede thing and compiles everything
Pentium-optimized, be aware that Pentium optimizations only make a big,
noticeable difference for the original and MMX Intel Pentium (not PPro,
not P2, not P3, not K6, etc.) processors.  The big speedup is because the
compiler/assembler reschedules integer instructions so that they can
execute in parallel inside the Pentium's two integer pipelines (which
have rather primitive inter-pipeline conflict/dependency resolution
hardware).  Most CPUs since then (Cyrix 6x86MX/M2, AMD K6-series, and
Intel P6-series including PPro, P2, P3, and Celeron) have better conflict
and dependency analysis/resolution hardware (or can execute
out-of-order), and don't gain much from Pentium-specific optimizations.
In fact, most other CPUs run better with plain old i386 or i486 code than
they do with Pentium-optimized code.

That said, Pentium optimizations *should* really help out owners of the
genuine Intel Pentium (and MMX) processors.  By virtue of the additional
flexibility for old machines, I'd be impressed to see Debian do this --
it would probably require resolving some of the same problems that hold
back a true segmentation of the distribution.  So, from an infrastructure
and making-the-distribution-amazing (as if it isn't already :)
standpoint, this is a good thing -- from a speeding-up-your CPU
perspective though, it's only a great thing if you have a true
made-by-Intel Pentium or Pentium MMX.

Anderson MacKay <mackay@rice.edu>

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