[GRLUG] Pentium 4 and Gentoo Linux?

[Adam Tauno Williams]

On Wed, 2013-06-19 at 18:11 -0500, Philip Robar wrote:
> I’m hoping that someone, like Mike Mol - our resident Gentoo advocate,
> might know the answer to this (and save me hours of experimenting):
> Will compiling Gentoo specifically for Intel P4/Netburst with GCC,
> Intel or LLVM make a noticeable difference on a general purpose
> desktop as opposed to using a generically compiled distribution?

I know next to nothing about Gentoo... but I'd be willing to wager lunch
that the answer is "No way, no difference".  I've seen more bugs
introduced by eager-to-optimize setups than I have performance
improvements.  Compiler optimization performance improvements are pretty
much limited to code written specifically to demonstrate they make
things go faster.

Note that you said ****"difference on a general purpose desktop"***.
Special cases, especially those involved math / real-data-processing
might be different, but a "general purpose desktop"... no way, no
difference.  You're more likely to break something.

> I found lots of articles comparing P4s vs other CPUs, but most are
> windows based and as such used precompiled benchmarks so they aren’t
> of any real help. I did find one article where compiling for P4 made a
> huge improvement for a specific math program (SPM (2)) and a short
> discussion about Arch Linux having optimized kernels (3). The latter
> lead me to an article that said, that at least for Core architecture
> CPUs, kernel optimization alone makes only a small,

No surprise; in most cases, and *especially* on a "general purpose
desktop" time spent tied up in kernel routines is limited.  glibc and
other common/core libraries would be more effective targets of
optimization.  But you are just as likely to break something.

>  but measurable difference using building the kernel as a benchmark.
> In short, Intel was able to keep competitive, in the absence of
> optimized binaries, by ramping up clock speed and cache size at the
> expense of power consumption and heat.

Nothing beats a BIG GUN. Hence the USS Mississippi. Cheap [relatively]
and effective.

> So, do any of the current compilers (Intel, GCC, LLVM) generate
> Netburst optimized code such that compiling Gentoo specifically for it
> would make a noticeable difference on a general purpose desktop of
> that era?

I'd crawl thier bug databases to see what turns up. Like
<http://gcc.gnu.org/bugzilla/buglist.cgi?query_format=specific&order=relevance%20desc&no_redirect=1&bug_status=__all__&product=&content=netburst>

More specific instruction set code names and the like would probably be
better search keys than "netburst" (which is rather more marketroidy
than technical).

> (I know that this question is completely irrelevant nowdays, but I’ve
> always been curious as to the answer.)

Nah, it isn't irrelevant at all if your interested in it. :)


-- 
Adam Tauno Williams <awilliam at whitemice.org>