Well since I had a crash 3 days ago I can tell you what my exerience with
CFLAGS:
First install:
Filesystem: ext3
-march=athlon-xp -O3 -pipe -funroll-loops
Note: according to gcc manuall, fomit-frame-pointer finline-functions and
all the cra is already turned on by O3
Second install:
Filesystem: reiserfs
-march=athlon-xp -02 -pipe
By accident I was already doing a little test of my own, on the first
install, startup time of konqueror, prelinked: 0,7s
second install had only 0,6s
Also the files, compiled binaries, libs were almost10% smaller. I guess
that's one part of the faster startup.
After studying the gcc manuall up and down I don't believe, that the gentoo
suggested O3 is not the best flag for compiling the whole distro, I think it
makes things much worse, only people should use that flag, who already know,
that they have certain functions in their programms that will benefit from
O3, which in most cases doesn't happen.
Also some poeple still believe, that they have to add 50 other flags to
their make.conf, cause gcc man shows them. Here is what gcc manual on their
HP says:
O3 contains:
-fforce-mem
-foptimize-sibling-calls
-fstrength-reduce
-fcse-follow-jumps -fcse-skip-blocks
-frerun-cse-after-loop -frerun-loop-opt
-fgcse -fgcse-lm -fgcse-sm
-fdelete-null-pointer-checks
-fexpensive-optimizations
-fregmove
-fschedule-insns -fschedule-insns2
-fsched-interblock -fsched-spec
-fcaller-saves
-fpeephole2
-freorder-blocks -freorder-functions
-fstrict-aliasing
-falign-functions -falign-jumps
-falign-loops -falign-labels -fdefer-pop
-fmerge-constants
-fthread-jumps
-floop-optimize
-fcrossjumping
-fif-conversion
-fif-conversion2
-fdelayed-branch
-fguess-branch-probability
-fcprop-registers
-fforce-mem
Force memory operands to be copied into registers before doing arithmetic on
them. This produces better code by making all memory references potential
common subexpressions. When they are not common subexpressions, instruction
combination should eliminate the separate register-load.
Enabled at levels -O2, -O3, -Os.
-fomit-frame-pointer
Don't keep the frame pointer in a register for functions that don't need
one. This avoids the instructions to save, set up and restore frame
pointers; it also makes an extra register available in many functions. It
also makes debugging impossible on some machines.
On some machines, such as the VAX, this flag has no effect, because the
standard calling sequence automatically handles the frame pointer and
nothing is saved by pretending it doesn't exist. The machine-description
macro FRAME_POINTER_REQUIRED controls whether a target machine supports this
flag. See Register Usage.
Enabled at levels -O, -O2, -O3, -Os.
-foptimize-sibling-calls
Optimize sibling and tail recursive calls.
Enabled at levels -O2, -O3, -Os.
-finline-functions
Integrate all simple functions into their callers. The compiler
heuristically decides which functions are simple enough to be worth
integrating in this way.
If all calls to a given function are integrated, and the function is
declared static, then the function is normally not output as assembler code
in its own right.
Enabled at level -O3
So guys please, don't fall for that CFLAG hype, most of these optimization
tales are just plain mystery and I'd say 99% of the people, that set CFLAGS
don't even know what they are doing, they read posts in threads then they
post them themselves and so on. It's just plain crap.
Set the right march and O2 and you won't loose over any other distro, if you
want fast startup times, prelink will do its job. Also you have to note,
that some distros use kernel patches that enhance speed, the kernel from
kernel.org ususally is very stable and works for most, but isn't very much
tuned to run for best performance.
----- Original Message -----
From: "Eric Marchionni" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Sunday, November 02, 2003 2:24 PM
Subject: [gentoo-user] bad gentoo performance
> hi
>
> what about that?
>
http://articles.linmagau.org/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=227
>
> cheers,
> eric
>
>
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>
>
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