-O3 vs. -O2 (was Re: [ale] sharing an experience....debian....)

[Jeff Hubbs]

There's another reason why I ask.  I frequently install Gentoo on slow
machines because a) I want to wring every last bit of performance I can
out of the hardware available and b) I'm not under time pressure to do
so :)

But, according to this, in doing so and accepting the -O3 optimization
suggested, I may only be hurting myself, ESPECIALLY if after building
gcc, glibc, etc. in the bootstrap phase with -O3 and subsequently
compiling everything else with that gcc, it might be taking m hours
(days?) longer than necessary.

I'd run tests. but I'd better do it on a CPU from this century or it'll
take so long I'll forget what I'm testing.

- Jeff

On Wed, 2004-02-11 at 22:37, Jeff Hubbs wrote:
> Can someone explain to me why the -O3 optimization would make programs
> run *slower*?  In asking, I'm not trying to cast aspersions or challenge
> the assertion, I'm really only just trying to ask how this is so.
> 
> - Jeff
> 
> On Wed, 2004-02-11 at 19:23, James Sumners wrote:
> > Stupid exmh didn't send this with the correct From: address earlier today.
> > 
> > >From the November 04, 2003 Debian news
> > (http://lists.debian.org/debian-news/debian-news-2003/msg00056.html):
> > 
> >  --- Begin Quote ---
> >  Debian faster than Gentoo? Matt Garman [2]wondered why his C++
> >  program ran dramatically slower when compiled on a Gentoo machine than
> >  when compiled with Debian Sid. He later [3]reported that recompiling
> >  the Gentoo C++ libraries with less aggressive optimization flags (-O2
> >  instead of -O3) eliminated the speed difference. Matt also [4]added
> >  that Debian and other distributions are conservative, but set up by
> >  very experienced people.
> > 
> >   2. http://article.gmane.org/gmane.linux.gentoo.user/50924
> >   3. http://article.gmane.org/gmane.linux.gentoo.user/50973
> >   4. http://article.gmane.org/gmane.linux.gentoo.user/50953
> >  --- End Quote ---
> > 
> >  Basically, Red Hat (Fedora) packages are typically compiled in a haphazard
> > fashion in relation to the other packages in the distribution. The packages in
> > Debian go through an arduous testing process and are built according to rather
> > strict rules.
> > 
> > James Sumners
> > 
> > On Wed, 11 Feb 2004 13:12:30 -0500
> > Keith Morris - IQ <keith at iqtv.com> wrote:
> > 
> > > Hi all, just wanted to share a quick experience and get your opinions if 
> > > you are willing.
> > > 
> > > I have been using linux off and on since Redhat 5.1 and exclusively for 
> > > the last 3 years at home.  I have pretty much been a redhat man with no 
> > > complaints.  I use Fedora Core 1 on my 2 main machines at home (both 
> > > 1.6GHz).  Well, recently I got a PIII 866 to play with and installed FC1 
> > > on it and the speed was really quite sluggish.  Played with a few more 
> > > distros which I wasn't really happy with.  Well, I've always been afraid 
> > > of Debian with it's infamous hell-installer, but with it's new Beta 
> > > installer, I decided to try it.
> > > 
> > > After a pretty painless net-install, I was totally shocked with the 
> > > speed of Debian.  Easily twice as fast as Fedora on the 866 using the 
> > > *SAME* software (Gnome 2.4, KDE 3.1.5, OpenOffice, Evolution, XFT 
> > > support, antialiasing, etc.) I still have not gotten the sound working, 
> > > but believe that I will be able to (with a few posts to the ALE list :)) 
> > > The only main difference is that I formatted / with reiserfs instead of 
> > > ext3 with FC1.
> > > 
> > > I was wondering if anyone could guess why debian would be sooooo much 
> > > faster with basically the same "Desktop" type of configuration? Do many 
> > > of you use Debian?
> > > 
> > > I will probably stick with Debian on this machine to learn about the 
> > > different ins-and-outs.  I absolutely *love* apt-get for debian.  I have 
> > > used it with rpms on redhat, but it seems better with debs...dunno...
> > > 
> > > Anyway, thanks for letting me share.
> > > 
> > > Keith Morris
> > > Creative Director
> > > Design / Effects
> > > IQ television group
> > > http://www.iqtv.com
> > > 
> > > 
> > > _______________________________________________
> > > Ale mailing list
> > > Ale at ale.org
> > > http://www.ale.org/mailman/listinfo/ale
-- 
Jeff Hubbs <hbbs at comcast.net>