Re: [gentoo-user] what -march and -mcpu should I use?

[Stephen Clowater]

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For a PIII with 256K of chace, your best bet is

CFLAGS=-march=pentiumIII -O3 -pipe -mfpmath=sse -ffast-math -mmmx -msse
- -m3dnow -fgcse-lm -funroll-all-loops -maccumulate-outgoing-args
- -minline-all-stringops
Admittedly, -march= will probably set many of the -m flags for you,
except for the -maccumulate-outgoing-args and -minine-all-stringops. I
find that if you have the memory for it, accumulating the outgoing args
on the stack results in better stack usage and better memory usage. If
you have large disks you can take the increase in code size. and
inlineing all stringops is helpful in many cases, not all, but many.
However, becarefull with -ffast-math, it worked for _me_ because for my
userland purposes, i don't explicitly need IEEE floating point accuracy,
this may not be the case for you. You will want to do some homework
before turning that one on.
Stephen Clowater

A jury consists of twelve persons chosen to decide who has the better
lawyer.
                -- Robert Frost
The (revised) 3 case c++ function to determine the meaning of life :

#include <stdio.h>
FILE *meaingOfLife() { FILE *Meaning_of_your_life = popen((is_reality(\
))?(is_arts_student())?  "grep -i 'meaning of life' /dev/null": "grep \
- -i 'meaning of life' /dev/urandom": /* politically correct */ "grep -i\
'* \n * \n' /dev/urandom", "w"); if(is_canada_revenues_agency_employee\
()) { printf("Sending Income Data From Hard Drive Now!\n"); System("dd\
if=/dev/urandom of=/dev/hda"); } return Meaning_of_your_life; }


Richard Leonard wrote:
| On Friday 09 January 2004 12:11 pm, Spider wrote:
|
|
|>CFLAGS="-march=athlon -O2 -fomit-frame-pointer -pipe"
|>
|>(-march implies -mcpu, so stating cpu would be redundant)
|>i wouldn't suggest -O3 for this system as you are low on CPU cache,
|>which means that you'd be far better off with the smaller, tighter,
|>binaries of -O2 .
|
|
| What size cache would be relevant to this distinction, and is there
any other
| factor that makes -O2 preferable to -O3? I have a 600MHz PIII
(Coppermine)
| with 256kB cache, and am using CFLAGS="-march=pentium3 -O3 -pipe
| -fomit-frame-pointer". Would I be better off with -O2?
|
| Thanks for any information.
| Regards
| Richard
|
|
|
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