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

Wed Feb 11 22:57:31 EST 2004

I think it really depends on if the original C/C++ was written with optimization
in mind. Most of the time that isn't even an afterthought considering today's
hardware and compilers. Someone who is more experienced with GCC should have an
infinitely better response than this.

Here is a decent article with good
references about GCC and the optimization
flags though: http://freshmeat.net/articles/view/730/

On 11 Feb 2004 22:44:19 -0500
Jeff Hubbs <hbbs at comcast.net> wrote:

> 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>
> 
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://www.ale.org/mailman/listinfo/ale

-- 

I used to be interested in Windows NT, but the more I see of it the more it
looks like traditional Windows with a stabler kernel. I don't find anything
technically interesting there. In my opinion MS is a lot better at making money
than it is at making good operating systems.  -- Linus Torvalds
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