CFLAGS determination script

s3ntient · Guru Joined: 13 Apr 2003 Posts: 304 Location: Lyon, France

Don;t know if this was posted before but here's a script that determines which CFLAGS are compatible with your PC:

genneth · Apprentice Joined: 24 Mar 2003 Posts: 152 Location: UK

On my Celeron(Coppermine) at least, it is greatly beneficial to have -mfpmath=sse,387 instead of just sse.

Great work!

lurid · Guru Joined: 12 Mar 2003 Posts: 595 Location: Florida

My Duron reports that I should be using -march=athlon-xp

I know it has the Morgan core, but I thought that ment it was basically just a tbird with less cache. Right now I'm using -march=athlon-tbird.

floam · Posted: Tue May 13, 2003 1:22 pm Post subject:

why would you use athlon-tbird for a morgan? didn't you know you have an athlon xp with less chache?

ixion · l33t Joined: 16 Dec 2002 Posts: 708

very cool stuff!! nice work!

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lurid · Guru Joined: 12 Mar 2003 Posts: 595 Location: Florida

piotraf · Posted: Tue May 13, 2003 6:32 pm Post subject: Re: -mfpmath=sse,387

Frozenwings · n00b Joined: 02 Apr 2003 Posts: 47

Hey, nice stuff! This is gonna come in handy when I change my
computer, as I'll need to change the CFLAGS too.
This has inspired me to write a CFLAGS selector using bash and Xdialog...

Woody · Guru Joined: 30 Nov 2002 Posts: 592 Location: Milwaukee

Its not clear to me (the gcc manpage is a little terse) that
a good deal of these options aren't taken care of by specifying
--march.

BTW, the script reports athlon-xp on my dual athlon-mp's
I wonder if there is much difference, but...

Could someon who really understands this stuff explain?

ta.

Gnufsh · Guru Joined: 28 Dec 2002 Posts: 400 Location: Portland, OR

-march=athlon-xp -mfpmath=sse -msse -mmmx -m3dnow
is what I get. Here is my /proc/cpuinfo:
processor : 0
vendor_id : AuthenticAMD
cpu family : 6
model : 8
model name : mobile AMD Athlon(tm) XP 1800+
stepping : 0
cpu MHz : 1499.962
cache size : 256 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 1
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse syscall mmxext 3dnowext 3dnow
bogomips : 2981.88

------
-msse -mmmx and -m3dnow are redundant because of -march=athlon-xp. And, the athlon's on board 387 floating point co-processor is better then the pentiums, and most FP math is faster using it, so -mfpmath=sse actually causes a performance hit (I tested this with several benchmarks).

fdavid

First of all, thanks for the nice script. I was always hasitating which flags to choose for my Celeron Tualatin. I have used simply i686 so far (family 6, model 11, stepping 1). The script though gave me a bit different result: -march=pentium3 -mfpmath=sse -msse -mmm

I've tried to find some info on the internet, but I haven't found the classification of my processor even on Intel's website. AFAIK it should be some p3. The best info what i could find is http://www.paradicesoftware.com/specs/cpuid/index.htm . But it also doesn't help me a lot.

I would be curious of the information source, on which this script is based. (It would be also interesting for the kernel configuration, where I use a secure avarege option, as well.)

Thanks,
fdavid

BradB · Posted: Tue May 27, 2003 9:43 pm Post subject:

Does anybody know if Gentoo has an index of CPU : CFLAGS that give the best performance? I know there have been many CFLAGS threads, but a webpage (or auto configure with this script at install) would help make the FLAGS choice easier.

Brad

Ian · Posted: Wed May 28, 2003 12:05 am Post subject:

i get

lurid · Guru Joined: 12 Mar 2003 Posts: 595 Location: Florida

The optimizations are basically your choice, so the script wouldn't deal with that. O2 seems to be standard, though I've heard good things about Os as well. Based on your output I'd do something like

axses · Tux's lil' helper Joined: 18 Mar 2003 Posts: 110

Have a look here for advanced cflags etc.

http://www.freehackers.org/gentoo/gccflags/flag_gcc3opt.html

Happy gentoo-ing :-)

thx for the script

fdavid · Posted: Wed May 28, 2003 8:13 am Post subject:

Gnufsh · Guru Joined: 28 Dec 2002 Posts: 400 Location: Portland, OR

A Celeron (Coppermine, Tualatin) is a p3 with less cache on a slower bus. I think the Tualatin Cellys even have 256k L2 cache. -march=pentium3 is probably the best. As for the rest, maybe -O2 -pipe -fprefetch-loop-arrays -mfpmath=sse,387?

robbat2 · Developer Joined: 19 Feb 2003 Posts: 82

I posted an annouce of this elsewhere before, but here it is again:
http://gentoo.slinky.surrey.sfu.ca/cflagcollect/
This is a gentoo mini-project to write a correct version of the script posted here, if everybody would please submit their cpuinfo data, it would help greatly.

Terminal · Posted: Thu May 29, 2003 11:52 am Post subject:

Well, the script works, although it is detecting my duron as being -march=athlon instead of being -march=athlon-tbird ... weird.
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fdavid · Posted: Mon Jun 02, 2003 2:57 pm Post subject:

LosD · Posted: Sun Jun 08, 2003 9:07 pm Post subject:

cromozon · Posted: Wed Jun 11, 2003 2:30 pm Post subject:

Im going to use this in a script that one day should be able to configure the kernel automatic, it's GREAT

CromoZon

BennyP · Posted: Tue Jun 17, 2003 8:14 pm Post subject:

I have a Pentium 3 (coppermine) 800.
cat /proc/cpuinfo gives me:

pi-cubic · Tux's lil' helper Joined: 25 May 2003 Posts: 143

edit your /etc/make.conf and add the missing parameters...easy, huh?

....thx 4 this very neat script!!!

but one question:
can you use the output also for your CXXFLAGS?

xunil · Posted: Wed Jun 18, 2003 4:32 pm Post subject: GCC 3.2 problems w/ P4 and SSE2

GCC 3.2 (the default GCC in Gentoo 1.4) generates bad SSE2 code. You should use -march=pentium3 for Pentium 4s and also omit -msse2 for GCC 3.2 and below, but GCC 3.3 fixes this.