CFLAGS Central (Part 1)

sleek · n00b Joined: 09 Jan 2003 Posts: 71

What would be the best CFLAGS line for my CPU based on the information below:

soaringcondor · Tux's lil' helper Joined: 16 Dec 2003 Posts: 103

Actually -Os will disable a couple of functions that -O2 enabled, other than that they are basically the same. Those functions speed up the program but in doing so increase the file size.

robmoss · Posted: Mon Feb 09, 2004 4:50 pm Post subject:

I'd be interested to see that gimp benchmark run with -O3 and with -O3 -ftracer and would wager that a significant speed boost would result. The -O* optimization levels are correct, and -O2 is still faster than -Os on a P4 in general. Check out Scott Robert Ladd's ACOVEA website. It should be clear to anyone that no amount of trying to actually work out how GCC works will result in a definitive answer even for a simple piece of code as to what will run the fastest; in fact, the interoperation of optimizations is enough to confuse a hardened GCC dev, no matter how much he/she knows about the architecture and operation of GCC. Evolutionary analysis is the only way to go...
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sapphirecat · Guru Joined: 15 Jan 2003 Posts: 376

rosinante · n00b Joined: 26 Dec 2003 Posts: 5

Some questions:

Which is the default compiler with gentoo: gcc 3.2.3 of 3.3.2 ?

Is -fpic mandatory for prelinking?

I have a pentium4 celeron with SSE/SSE2/MMX capabilities; does GCC *effectively* passes these options with '-march=pentium4' ?

I have a very small L2 cache (128KB) and limited ram (128MB, shared for video), what would be optimum:
-'Os' with '-mftpmath=sse' and '-funroll-loops'
or
-'O2' with '-mftpmath=sse'

Are '-finline-functions' and '-frename-registers' any good on my low-performance box?

Any pointers are greatly appreciated - this gcc-tweaking is a mess :)

robmoss · Posted: Mon Feb 09, 2004 9:14 pm Post subject:

sapphirecat · Guru Joined: 15 Jan 2003 Posts: 376

rosinante · n00b Joined: 26 Dec 2003 Posts: 5

Nutterpc · Tux's lil' helper Joined: 02 Feb 2004 Posts: 83

Good day to one, good day to all

I reckon making the move to Gentoo for me was wise, considering my tweaking background on windows, I thought gentoo would be the best one for me to use :wink:

.......as that's what it's all about, tweaking your linux distro to how you like it

Anywayz, my CFLAGS I use are as follows

-march=athlon-xp -O3 -fforce-addr -fomit-frame-pointer -foptimize-sibling-calls -fthread-jumps -fgcse-lm -fgcse-sm -frename-registers -mmmx -m3dnow -msse -mfpmath=387 -ffast-math -fmerge-constants -fnocprop-registers --param max-gcse-memory=512

I've had no probs with this string, me own one....and on a Barton core XP2500 it absolutely hoons :twisted:

, plus having a Gb of DDR400 Kingmax in Dual Channel might also have something to do with it, heeheeheeheehee :lol:

Will modify it as I see more ways to get speed outta gentoo

Nutterpc
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nmcsween · Guru Joined: 12 Nov 2003 Posts: 381

Alright Im not a gcc developer but wouldn't it be better to -falign-functions to equal 64? the L1 cache on the athlon xp is 64kb and since most code will be exchanged in maybe 1 or 2 cycles with the L2 cache so why go with 16?

tapted · Posted: Wed Feb 18, 2004 10:12 pm Post subject:

robmoss · Posted: Thu Feb 19, 2004 12:07 am Post subject:

A brief attack on the acovea sources and a recompile suggests precisely no difference whatsoever with -falign-*=2^n, n integer, n <= 6, * functions / loops / jumps, except for a performance hit when they're all set equal to 1.

So set them to whatever the hell you want, it makes no difference.
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Reality is for those who can't face Science Fiction.

emerge -U will kill your Gentoo
ecatmur, Lord of Portage Bash Scripts

tapted · Posted: Thu Feb 19, 2004 3:34 am Post subject:

robmoss · Posted: Fri Feb 20, 2004 4:49 pm Post subject:

C1REX · l33t Joined: 02 Jan 2004 Posts: 774 Location: Poland/UK

Hi
Here In Poland there's a bit different fashion as far as flags are concerned, and you can come across a bit different solutions. For instance I'll give mine for Duron 800. They look a bit exotic here, but in Poland they can be regarded as pretty standard. It isn't very popular to meet O3. Os and O2 mostly.

t0mcat · Posted: Mon Feb 23, 2004 6:28 pm Post subject:

lo all,
i'm a noob to the penguin os, i've recently installed gentoo and made the bootstrap with CFLAGS="-march=athlon-xp -O2 -pipe".

i've read so many stuff about CFLAGS that i'm really confused, btw after many hours spent reading everywhere, now i'm about to "emerge -e world" with this:

CFLAGS="-march=athlon-xp -O3 -pipe -fomit-frame-pointer -ffast-math -fmove-all-movables -funroll-loops -fprefetch-loop-arrays -fforce-addr -mmmx -msse -m3dnow -mfpmath=387 -frename-registers -maccumulate-outgoing-args"

i've got an athlon-xp barton 2500@3200.

hope everything will be ok.

btw i've got a n00b question about recompiling the whole mess:
can i "emerge -e world" from an X terminal (gnome)? i'd be quite bored having the pc occupied for more than a whole day, so i'd like to surf or chat while the cpu does such a huge work. Or shall i do it necessary from the console after a simple boot, without loading any D.E.?

ta for any reply.
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AnonimoVeneziano · n00b Joined: 25 May 2003 Posts: 65

Hi all

I'm just installing Gentoo Now , and I'm doing the bootstrap in this moment (I'm posting from Links

)

Anyway , I've compiled with :

"-O3 -mcpu=athlon-xp -march=athlon-xp -fomit-frame-pointer -momit-leaf-frame-pointer -fprefetch-loop-arrays -mfpmath=sse -fforce-addr -pipe"

I would also add "-ftracer" , but gcc 3.2.3 (that is in the base CD) doesn't support this option and I'll add that after bootstrapping gcc 3.3.2 .

I've added -mcpu=athlon-xp because I've heard that some ebuilds filter the -march option ,is this true? Anyway -mcpu shouldn't change the binary created by the compilation with only "-march" , because "-mcpu" is a subset of "-march" , that's right?

Thanks

Bye

Marcello

nmcsween · Guru Joined: 12 Nov 2003 Posts: 381

I don't see the use of putting -mcpu=* since that is exactly the same as the i-686 setting in CHOST and -march=* turns on that flag as well so it would just be a waste of typing.

seppe · Posted: Tue Feb 24, 2004 5:06 pm Post subject:

Hi, I have a pentium 3 800Mhz, and I tried these CFLAGS:

CFLAGS="-O3 -march=pentium3 -fprefetch-loop-arrays -funroll-loops -pipe -fomit-frame-pointer -fforce-addr -fmove-all-movables"

and it's still compiling after a 'emerge -e world'. I tried the same CFLAG first with -freduce-all-givs (which gains 35% of speed at a pentium3, I read here) but I get an error when it tries to compile python2.3 (parallel make error, or something).

Now my questions:
1) Do I gain much speed with my current CFLAG? (I had the standard 'safe' pentium3 CFLAG first which was suggested at the freehackers site)
2) How can I compile everything with the -freduce-all-givs? I mean: when it fails at python2.3 during a 'emerge -e world', can I compile python only without the -freduce-all-givs flag and continue my 'emerge -e world' without starting all over again? If so, how do I do this?
3) Will -mfpmath=sse,387 gain much speed? And is it safe? Do you suggest me to use it, or is the increase of speed marginal to risk this?
4) How can I use the acovea program with gcc 3.3.3? I get always 'compilation failed' and a segmentation fault when I should get my 'best' CFLAGS, and can I use acovea with 'emerge -e world'?

Thanks for replying in advance, but keep it simple ... I'm a CFLAG n00b

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Malakai · Apprentice Joined: 24 Dec 2002 Posts: 299

[quote="robmoss2k"]

Penguin_Biker · Posted: Wed Feb 25, 2004 2:31 am Post subject:

Athlon XP 1700+

i'm also having a problem with -freduce-all-givs

here's my CFLAGS

tapted · Posted: Sat Feb 28, 2004 8:04 am Post subject:

tapted · Posted: Sat Feb 28, 2004 8:10 am Post subject:

spaetz · n00b Joined: 15 Dec 2003 Posts: 16

til · n00b Joined: 02 Mar 2004 Posts: 7

I also need some help, cause i habe the same problem, like others - but I thought my CFLAGS were just optimized for my system (Athlon XP 2200+). But anyway my gentoo crashes after compiling for about 3 hours.

For your help, my cflags: