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From: "matt c" <matt@legalizefreedom.org>
To: "gentoo-dev ML" <gentoo-dev@gentoo.org>
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Date: Thu, 14 Aug 2003 10:38:47 -0700
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Subject: Re: [gentoo-dev] "Distro Day (Measuring the benefits of the Gentooapproach)"
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Sorry for butchering your email, I only wanted to ask the list about one
point I saw that you made.

----- Original Message ----- 
From: "William Kenworthy" <billk@iinet.net.au>
Subject: Re: [gentoo-dev] "Distro Day (Measuring the benefits of the
Gentooapproach)"
<snip>
> Wish more would do as you have done - I dont think too many follow this
> approach.  Most seem to just do the reccomended, or go for the max.  I
> did a few key apps, made my choices and have stayed with them.  If a
> really useful cflags project gets up, it would be nice to run it
> regularly and perhaps find that the new gcc just emerged gives a
> measured 5% speed up if you use the new -supercharger flag!

I think that this is where the confusion with many "experts" on optimization
lies. What is a good program to use as a benchmark for optimizations and
compiler flags? How does one measure the performance gain? Is the
performance gain just in load time, or in processor usage throughout the
program? Do the benefits of using a particular optimization translate from
one program to the next? Some programs are snappier with -O2, some perform
twice as quick with -O3. Who is to say? How does one know for certain?

 I have found that, for the most part, -O2 compiled apps runs much faster on
my system. I don't have any hard numbers, but I do know I decided to rebuild
my system recently with just -O2 ,-pipe, and -fomit-frame-pointer only -
Everything I do seems to be a bit more responsive.

>>From what I've been hearing, I think the general consensus is that -O2 seems
to be a better optimization than -O3 *in general, for the most people*, yes?
Right now the "Decent examples" in make.conf include (in both examples) -O3
as the optimization level to use. If -O2 is that much better, would it not
be the sane thing to recommend to users who read make.conf to use -O2?

I don't know - do -finline-functions and -frename-registers really make that
much of a difference? I am no expert at compiler internals. I only know what
has been my experience and what others say.

Just a thought.

Matt



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