CFLAGS Central (Part 1)

augury · l33t Joined: 22 May 2004 Posts: 722 Location: philadelphia

CFLAGS="--param max-unrolled-insns=16 -fsingle-precision-constant -DNO_DEBUG -g0 -funroll-loops -ffast-math -finline-limit=4096 -march=pentium4 -fomit-frame-pointer -pipe -ftracer -O3 -fmerge-all-constants -fprefetch-loop-arrays"

CXXFLAGS="-fabi-version=0 -ffunction-sections -DNO_DEBUG -g0 --param max-unrolled-insns=16 -funroll-loops -ffast-math -finline-limit=4096 -march=pentium4 -fomit-frame-pointer -fprefetch-loop-arrays -pipe -fsingle-precision-constant -ftracer -O3 -fmerge-all-constants -fpermissive -fno-enforce-eh-specs"

I've been used these flags to compile boxes with gcc-3.3.3 and gcc-3.3.4 and they've worked well on almost all ebuilds.

gcc won't build with -DNO_DEBUG and -g0 because it uses the debugger to build itsself backwards. i dont think it allows -fsingle-precision-constant to go through the autoconf either.

glibc won't let ffast-math through and --param's get bjorked in its makefiles somehow. same thing happens in openoffice but only on one section.

usually if a module specificly needs double precision it stops and the the compile script can be cut and pasted minus -fsingle-precision-constant. when the modules built the ebuild can be resumed with no harm done (anyone know if theres a way around this?). java-script decides weather or not to use single or double precision at run time though so it can be broken but not stop the build. kjs in kdelibs and mozkjs (i think) in mozilla (and thunderbird and firefox) are the only js engine i know of.

tetex can be broken by O3 sometimes.

i use --param max-unrolled-insns=4 for pentium3's , only because intel says that those are the most loops that do any good and i figure they'd know. i dont even know if its loops or instructions in the that im limiting but it keep the bloat down a little and should still allow for loop prediction. my desktop runs nicer than windows ever did so i guess im happy enough compiling this way.

augury · l33t Joined: 22 May 2004 Posts: 722 Location: philadelphia

oh yeah. i tryed gcc-3.4.0. it compiles much faster and everything runs faster but it seem like things got mixed up with two different runtimes. i remember kdedev couldn't link properly. i dont know if its something i did or if the aclocal files and such needed to be rebuilt or what.

blackcat4 · n00b Joined: 27 Nov 2003 Posts: 8 Location: UK

I've written a small script to test different cflags combinations (or even differnent versions of gcc). If anyone is interested, it's at:

http://blackcat.ca/dist/bench_gcc

To see how to use it, run it with:

Isaiah · Guru Joined: 25 Feb 2003 Posts: 359

drakkan · Apprentice Joined: 21 Jun 2004 Posts: 232

hi all

I'm buying a new laptop I choseed a pentium M 735 (1.70 GHz, 2 MB L2
Cache, 400 MHz FSB), my problen is what cflags I must use.
I read a lot of things, my conclusion is that for pentium M the best cflags
are the following:

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=pentium3 -pipe -O2 -fomit-frame-pointer -fforce-addr
-frename-registers -fprefetch-loop-arrays -falign-functions=64"
CXXFLAGS="${CFLAGS}"

I would like to choise -O2 because I read that the best optimization (-O3)
produce binary of great dimension and so the application are slow to start;

If I use gcc3.4 (I change make.profile link
to /usr/portage/profiles/default-linux/x86/2004.2/) I can use
-march=penitium-m ?

Actually I have a P3 1Ghz 512Mb Ram Geforce2 Go 32Mb, I have compiled gentoo
from stage1 with the following make.conf:

CFLAGS="-O3 -march=pentium3 -pipe -fomit-frame-pointer"
CHOST="i686-pc-linux-gnu"
CXXFLAGS="${CFLAGS}"
MAKEOPTS="-j2"
USE="-gtk -gnome qt kde alsa samba acl php perl cups mysql pam-mysql imap
libwww maildir sasl ssl"
FEATURES="sandbox strict sfperms"
LINGUAS="it"
ALSA_CARDS="maestro3"
GENTOO_MIRRORS="http://www.die.unipd.it/pub/Linux/distributions/gentoo-sources/"

some application such as mozilla seems slow to start (dma is enabled); I
thinks for -O3 option. Is corretct to use -O3 or -O2 in make.conf and then
build application such as mozilla, openoffice with -Os to reduce startup
time? For other huge package such as xorg or kde the default make.conf option
are ok or also in this case -Os is better then -O3?

Somebody tells pkg are the best choise because the system is up in few time
and this packages are built by expert developers and so they have package
specific build options that optimize them and make a very speed system, isn't
it?.

I'm very confused so I would like to have the opinion of
gentoo's expert.

Thanks
drakkan

d4n1el · Tux's lil' helper Joined: 21 Jun 2004 Posts: 76

I think I don't have optimizied settings... if someone knows what is best, i will be glad for some advices...
I've got a Athlon xp 2500+ Barthon

My setting is:

spb · Posted: Sun Sep 12, 2004 12:11 pm Post subject:

nxsty · Veteran Joined: 23 Jun 2004 Posts: 1556 Location: .se

el_compa · n00b Joined: 28 Jan 2004 Posts: 65 Location: France

Hi, I've got a Celeron @2.2GHZ (P4 core) system, 628MB in RAM.

I'm using gcc 3.4.2-r1

My CFLAGS are:

CFLAGS="-O2 -pipe -ftracer -march=pentium3 -fmove-all-movables -fomit-frame-pointer -fprefetch-loop-arrays"

I'm using -march=pentium3 because of crashes with qt apps.

Please, can anyone comment on these CFLAGS. I used to use these (and more flags) because I found them using acovea, but for gcc 3.3.x. Right now I dont want to let the machine run acovea for three days to find the best possible flags, so I'm hoping someone else has

.

Thnks,

Mario

AceOfAces_TS · Posted: Mon Sep 13, 2004 9:38 pm Post subject: AthlonXP-m

What would you do for a Athlon XP-m (moble) with 512mb ram on GCC 3.3?

Heres a /proc/cpuinfo

nxsty · Veteran Joined: 23 Jun 2004 Posts: 1556 Location: .se

Deranger · Veteran Joined: 26 Aug 2004 Posts: 1215

Currently using:

robmoss · Posted: Sat Sep 18, 2004 8:43 am Post subject:

Don't know if anyone's bothered, but if you're using GCC 3.4, these are very well tested, as I'm a gcc-porting dev and these are mine. Nothing should break. For my Athlon XP:

LockeAverame · Tux's lil' helper Joined: 14 Jul 2003 Posts: 108

i would suggest -funroll-loops in nearly all benchmarks it gives a 10% or more speedup.
mostly -O3 is faster than -O2 but not in all cases. with some benchmark rotations where i test with freebench and nbench with different cflagcombinations automatically, i found that -mfpmath=sse gives a 3% optimization. all numbers mentioned here are averages over all testcases in these benchmarks. -ftracer is mostly doing not very much, the same is right for -fmove-all-movables.
-ffast-math should only be used if you know what you are doing.
my cflags for athlon-xp and gcc-3.3.4 are:

-O3 -march=athlon-xp -mfpmath=sse -ffast-math -fmove-all-movables -fomit-frame-pointer -fprefetch-loop-arrays -ftracer -funroll-loops -pipe

everything works fine. with gcc-4.0.0 -fmove-all-movables should be erased from this, because it has a new vectorizing and peeling loop-unroller.
the binaries get bigger, but many people underrestimate a 512KB cache of a barton core, it's huge if you think of functions. gcc-4.0.0 will improve many parts of code, but its a pity that some optimizations wouldn't make it in, especially the aligning part. i hope that the vectorizer will do a good job. i will do some tests after a stable release comes out. upgrading to gcc-3.4 would be done if some big regressions are fixed.

KayZee · Posted: Sun Sep 19, 2004 7:23 pm Post subject:

If I make changes to CGLAG values in make.conf, do I have re-compile everything with the new CFLAG values? Or can the existing packages use the CFLAGs they were compiled with and new or updated packages use the new CFLAG values? Will Gentoo become unstale if mixed CFLAG values are used?

--Karl

LockeAverame · Tux's lil' helper Joined: 14 Jul 2003 Posts: 108

no, mostly it won't affect your system. only some flags like -malign-double or other aligns which destroy the normal binaryformats will lead to problems in this manner, but you shouldn't use these flags in your system either, they should only be used for special applications like numbercrunching which don't need to link to existing libraries.

Gentree · Posted: Wed Sep 22, 2004 3:37 pm Post subject:

tcbounce

Hello,

I heard -fstack-protector is always on in hardened gentoo profiles.

Is it safe to use this option with higher optimisation than -O2. I read that using higher than -O2 can break things at runtime and during linking. The Debian and LinuxfromScratch boys and girls have been talking about it.

http://www.trl.ibm.com/projects/security/ssp/node4.html <- see optimization section update June 2004

Cheers,

Luke

asph · Posted: Wed Sep 22, 2004 5:28 pm Post subject:

my new cflags for gcc 3.4.1-r2

LockeAverame · Tux's lil' helper Joined: 14 Jul 2003 Posts: 108

http://www.trl.ibm.com/projects/security/ssp/node4.html only says that some protections can't be established, and mostly the code doesn't get crappy except of xorg-x11 which doesn't like -fstack-protector at all (modules fail).
most of the optimizations shouldn't kill the stack-protection (even though it is not of very much help, but better than nothing).
-mtune is the same as -mcpu, there is no magic behind it.
and after all it's not a good idea to tune your system to a behaviour you don't know. mostly it's very annoying if people use flags like -ffast-math or -malign-double without knowing anything about their meaning.

Gentree · Posted: Thu Sep 23, 2004 12:33 am Post subject:

blackcat4 · n00b Joined: 27 Nov 2003 Posts: 8 Location: UK

Larcen · Apprentice Joined: 21 Mar 2004 Posts: 174

I've been using the same CFLAGS since I first built my Gentoo, sadly I never thought about changing them. Other than the -fomit flag, can anyone else recommend flags to help speed my Machine along? Also, should I upgrade GCC to a masked version, other than latest stable? If so, which ebuild?

Current Flags:

gentood · Apprentice Joined: 16 Mar 2004 Posts: 157 Location: Sweden