CFLAGS Central (Part 1)

seppe · Posted: Wed Mar 17, 2004 4:17 pm Post subject:

ok, thanks for your reaction ... I'll try those CFLAGS, but first I'll try to emerge binutils with these cflags, because I had problems before with binutils when I specified -freduce-all-givs.

If anyone thinks those CFLAG's ultraoctane.com gave are NOT good for my system for some reason, please tell me

I have also some other questions:
1) If I do an emerge -e world, can I stay in Gnome while it's recompiling my system? Or do I have to shut down Gnome and X completely and to the emerge -e world in my console?
2) How can I unmerge KDE with all his dependencies (which are not needed by other packages), because I don't use KDE anyway so I don't want to reëmerge it again.
3) If emerge -e world fails, can I resume succesfully with 'emerge --resume'? Has anyone have experience with this?
Thanks

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seppe · Posted: Wed Mar 17, 2004 5:32 pm Post subject:

some comments on the CFLAGS you suggested me:

nmcsween · Guru Joined: 12 Nov 2003 Posts: 381

Remember these are HIGHLY optimized flags and some packages won't compile with them. You'll need to take out a flag or two to get some packages to compile, try this on compiles that fail -march=X -O2 -pipe -ftracer -fno-crossjumping -maccumulate-outgoing-args -fmove-all-movables -freduce-all-givs if it's still giving you problems then you know it has to do with one of the last three.

seppe · Posted: Thu Mar 18, 2004 8:40 am Post subject:

Ok thanks,

I started the recompiling of my system yesterday and it's still going .. wish me luck

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carpman · Posted: Fri Mar 19, 2004 12:11 pm Post subject:

Hello, can any tell me if the settings i have for my pentium 2 366 mobile are ok or can be improved, cheers.

-march=pentium2 -02 -pipe fomit-frame-pointer -mmmx - funroll-loops -fforce-addr
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MG-Cloud · Apprentice Joined: 28 Oct 2003 Posts: 200

Hi,
From reading this thread (took *forever*), I've come up with the following cflags for my athlon-xp machine:

My current flags:
-march=athlon-xp
-mcpu=athlon-xp <- for ebuilds that strip -march
-O3
-pipe
-fomit-frame-pointer
-ftracer

Flags I plan on adding with a couple questions. Basically, the gist of my questions are - are these generally beneficial, or can they have detriments in a large number of applications as well? I dont' mind stability problems (eg re-emerging individual packages once in a while). I do however mind slowdowns that aren't immediately attributable to a certain cflag.

-funroll-loops
-fprefetch-loop-arrays

-mfpmath=387 (Big question here that I'd really like answered: Does this really speed things up on athlon xps? prior to reading this thread, it was my understanding that the sse instruction set included optimizations, and even if the athlonxp's sse implementation was less than optimal, it would still be faster than -mfpmath=387.)

-freduce-all-givs (heard this caused problems with binutils. is it okay now?)

Flags I may add, but am a little hesitant over. Eg - I've seen them mentioned once or twice in this thread, but have never really encountered them elsewhere. Any info about these would be great (I'm not too great with technical cpu details though, that's why i can't read the gcc manpages)

-fmove-all-movables
-fforce-addr

Thanks for any help! ^^

MG-Cloud · Apprentice Joined: 28 Oct 2003 Posts: 200

@carpman:
I'm a bit of a newbie here myself, so can't help you too much. Just wanted to point out one thing though - your cflags include -02. This is a typo - the correct option is -O2 (capital 'o'), not -02 (zero).

@seppe:
Good luck !

carpman · Posted: Sun Mar 21, 2004 3:36 pm Post subject:

seppe · Posted: Sun Mar 21, 2004 4:26 pm Post subject:

Well, it's still going (still something like 128 packages to go

), I've had some problems with a few packages but changing lowering my cflags for those packages, compile them and resume with the more extreme cflags works like a charm.

Though, some packages broke and lowering my cflag's didn't work, but there is still 'emerge --resume --skipfirst' to skip those packages

There was a problem with some assembler instructions, I think. But I wrote the packages' name down, and I'll try to compile them again when the rest is finished.

Also, I had problems with 'icc' in my use flags with some packages, but changing that to '-icc' did the job.

Mono gave me some problems too, but I think the compilation will succeed with less extreme cflags. But I do that later (so I used emerge --resume --skipfirst again), because I really want to finish the 'emerge -e world' as soon as possible.

Greetz and thanks again for the info

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seppe · Posted: Mon Mar 22, 2004 12:48 pm Post subject:

Gooberslot · n00b Joined: 27 Apr 2003 Posts: 26

I have a coppermine based Celeron and I was wondering if anyone had any suggestions for which cflags to use. Last time I tried installing Gentoo I used -march=pentium3 and -O3 and KDE wound up being very slow, much slower than the same version under Knoppix. I thought maybe -O3 was increasing the code size too much considering I only have a 128k cache and that maybe -O2 would be better. Any other options I should add?

mahir · l33t Joined: 05 Dec 2003 Posts: 725 Location: London

hi all
i have been reading they 12 pages of the 29in this topic
and i cant go no futher

could someone help me with a quick cut/paste..

what would be the optimal settings for my system?
i got a p4 HT 3.06ghz system with 512 ram.

any ideas please?
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Andrej · n00b Joined: 04 Oct 2003 Posts: 60 Location: Latvia

I'm use -03 -pipi -fomit-frame-pointer. What Óflags can i add? System Celeron 1300

nmcsween · Guru Joined: 12 Nov 2003 Posts: 381

Read
Run this program called acovea in simple terms it runs a few tests to figure out what will run best for your cpu ( takes about 48 hours ).

codergeek42 · Posted: Fri Apr 30, 2004 1:19 am Post subject: What CFLAGS to use?

My current CFLAGS (have not had problems):

robmoss · Posted: Fri Apr 30, 2004 1:22 am Post subject:

Yes - check out that thread you just started. Like I said, -O3 will be faster than -Os on your processor, as yours isn't a handheld, ARM, old PPC or SPARC, or 486 or earlier. Oh, I assume it's not an SMP system either. So -Os would be worthless for you.
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nmcsween · Guru Joined: 12 Nov 2003 Posts: 381

I just thought I would post my current CFlags running gcc 3.4:

phex · n00b Joined: 08 Jun 2002 Posts: 32

my current cflags are
-march=athlon-xp -mcpu=athlon-xp -Os -pipe -fomit-frame-pointer -fforce-addr -ffast-math -ftracer -fprefetch-loop-arrays

havent noticed any problems going AWOL or crashing. Except for every now and then I might come across 1 or 2 apps that won't compile with the -ffast-math enabled. Other than that everything seems fine. I've been using them on my box for almost a year now. Also the option
-fprefetch-loop-arrays is disabled at the -Os level. I usually may switch back to -O2

--------
CPU
Athlon XP 2500+ OC'd @ 3200+

kilrogg · Posted: Tue May 25, 2004 11:39 am Post subject:

-Os Level really only is for environments where code size is more important than speed as it optimizes binary size

I ran acovea on multiple computers (Pentium and AMD) and did speed tests with compiled applications such as LAME (mp3 encoder).

My optimized flags made LAME encode my reference MP3 in 10 seconds less time (2:21 -> 2:11). And i already did use the optimized flags described in gentoo install documentation.

I'm using the following flags:

-mcpu=athlon-xp -march=athlon-xp -pipe -O3 -ffast-math -maccumulate-outgoing-args -ftracer -funroll-loops -fprefetch-loop-arrays -fomit-frame-pointer

(-mmx, -m3dnow, etc. are automatically activated when using -O3)
For a complete help on gcc settings try 'man gcc'.

I encountered only 2 errors when recompiling my whole system (>500 packages) and I'm not sure they were compiler errors.

Whole system runs smoothly and very fast.

thechris · Veteran Joined: 12 Oct 2003 Posts: 1203

from what i've got so far on the athlon-xp:

-mfpmath=anything never comes up good, always neutral or bad. so leave this out.
-fomit-frame-pointer comes up equally good and bad...
-ftracer is good, but not overly so. never bad though.
-fprefetch-loop-arrays is usually very good, but in my experience, some programs don't like it...
-fstrict-aliasing came up very good as well.
-fstrength-reduce came up very good, and i think it's implied by -O2
-funroll-loops sadly came up mostly bad.
-fgcse also comes up as good.

right now i'm testing the aligning. so far:
-falign-functions=4
-falign-loops=1
-falign-jumps=4
-falign-labels=4

i suggest doing -O2 -finline-functions because some programs override -O3, and function inlining is usually better then worse.

and the things in -ffast-math usually help out as well.

MrPixel · Posted: Thu Jun 24, 2004 9:37 pm Post subject:

I just ran the ACOVEA huffman and tree benchmarks. They returned:
huffman:

josephoenix · Posted: Fri Jun 25, 2004 3:24 am Post subject:

I'm not sure if this is the place to ask this, but I am installing gentoo (again) and I am unsure of what would be the best cflags for this:

robmoss · Posted: Fri Jun 25, 2004 9:58 pm Post subject:

Ah, you git, I've got one of those on the way... I hope. Ordered it a month ago today. And it still isn't here!

Anyway, it depends - what version of GCC are you planning on using? If you're using 3.4, don't combine -O3 and -ftracer, as it causes problems.
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semiSfear · Guru Joined: 08 Jul 2003 Posts: 302 Location: Adelaide, SA

Does it matter where in CFLAGS you put the -pipe option? For example I got this in my make.conf file: CFLAGS="-march=athlon-xp -pipe -O3 -fomit-frame-pointer"

Does it matter if it looks like this:

CFLAGS="-march=athlon-xp -pipe -O3 -fomit-frame-pointer"

or if it looks like this:

CFLAGS="-march=athlon-xp -O3 -pipe -fomit-frame-pointer"

?
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zaanpenguin · Apprentice Joined: 01 Jul 2003 Posts: 203