Compiling optimization settings

[flick]

Hi, everyone!

Just did a fresh install of 3.4 loop3, checked out /etc/make.conf, and noticed that -Os was used instead of -O2 as in 3.3

I know that -Os is intended to optimize more for size than performance. Just curious if the Sabayon devs, or anyone more experienced with Gentoo and/or Sabayon, had any thoughts on stuff being compiled with -Os rather than -O2. Reason being, I was about to rebuild my system, tailored to my hardware. Did it with 3.3, sure I can do it again.

So, any thoughts, anyone?

[WarraWarra]

Think -O2 is better option can not remember why / long time ago. Should be optimization / cleaner if higher number ?

-j3 - s for makeopts or cpu+1 = -j2, dual core+1 = -j3 adds a lot of speed as well as -pipe after "-O2 -march=prescott -pipe" paralle fetch si good for slow inet connection but can be cheated by first downloading all files and then compile from a repository ?

Somehow -j16 -s has worked for my core duo t2600 2.16ghz laptop cpu but -j5 locksup ?
No one has explained or updated the -j options yet as surely they where put in place for a 486 or 586 cpu so a core duo is 8x or 12x 586 cpu's equivalent or 16x 486 cpu's ?

If you can google for your cpu and make options then the most fine tuned ones should be out there and you can copy them , also helps to know if a option is safe and tested before trying to fry a cpu LOL

Hope this helps.

[nikaya]

http://www.gentoo.org/doc/en/gcc-optimization.xml

[dawn`chorus]

Here's a spot where you can find safe CFLAGS for your architecture.

http://gentoo-wiki.com/Safe_Cflags

What are CFLAGS?

http://gentoo-wiki.com/CFLAGS

[flick]

Thanks, all. I have read those pages/sites you've all linked. Sorry I wasn't clear enough in my original post : any anecdotal evidence re : compiling with -Os versus -O2? Anyone here happier with one or the other, and why?

[dawn`chorus]

-O2 has been very good for me. Quite stable, which is my thang.

-Os optimizes for size. -Os enables all -O2 optimizations that do not usually increase code size and performs further optimizations designed to reduce code size.

-Os is very useful for large applications, like Firefox, as it will reduce load time, memory usage, cache misses, disk usage etc. Code compiled with -Os can be faster than -O2 or -O3 because of this. It's also recommended for older computers with a low amount of RAM, disk space or cache on the CPU. But beware that -Os is not as well tested as -O2 and might trigger compiler bugs.

Note that only one of the above flags may be chosen. If you choose more than one, the last one specified will have the effect.