On Tuesday 18 November 2003 05:44, Jason Stubbs wrote: > On Tuesday 18 November 2003 09:57, Chris Graves wrote: > > interesting article about selecting gcc optimizations (found on > > OSNews.com). > > > > http://www.coyotegulch.com/acovea/index.html > > Quite a good article! Shame it doesn't apply to us. I can't remember > where I read it, but the gcc crew were talking about doing an > overhaul (or at least an investigation) into -O1 -O2 and -O3. As > previous informal benchmarks done by Gentooists show, with the > current GCC compilers (including 3.3) -O2 can often produce faster > code than -O3. This is meant to have been addressed in 3.4.
And this applys to Gentoo expecially, because the whole system is compiled with those flags. In the tests the only ones that was compiled with the said flags were only the test applications. To make real optimizations one should first compile glibc with those different optimizations and then for these glibc versions the applications with different optimizations. Which makes it even more complex problem. Oh and by the way the testing was done in steril system. How does the comilation of those unrollinbg affect on desktop systems where there are multiple programs running? So cache trashing comes even easier and thus slows down every process... So now we need multiple hard disks, which every one has the exact same Gentoo system, but compiled with different optimizations. Then simply make the system boot so that the system is ran from our 2GB of memory so that different HD speeds doesn't affect the tests. :) > On the other hand, the code for his tester can be downloaded and then > modified only cover gcc33/32 optimizations. Anybody know of a few > noninteractive benchmark programs that could be tested with? I'm > happy to run some tests and publish results for AthlonXP using gcc33. The most distracting point in his teest was the fact that all tests were running in isolated environment ie no other running processes. This lets the whole 11k instruction cache of P4 for the one process, so that the penalty of unrolling and inlining raises quite a bit from normal desktop systems. I thus think that usefull tests can only be made in an environment resembling the real use situation. So the test made would suit for compile or rendering farms, but not for desktop environment. -- [EMAIL PROTECTED] mailing list
