Best CFLAGS for low memory/load times?

[sindre]

What would be the "best" CFLAGS to use on a computer with low memory, but a descent processor? Also the HD is quite slow, so I suffer from low memory and long load times.

Which is better? -Os, -O3 or -O2? Any other important flags? Any gain if I use glibc-2.3.2_pre1 over glibc-2.3.1? I also plan to use prelinking.

Grateful for any input.

[PT_LAmb]

I don't know much about the subject, but can tell you the following:

-O3 and -O2, are speed flags, setting one of them will optimize the binary to be a bit faster then a standard compiled one. I once read that -O3 doesn't improve much over -O2, can anyone confirm this?

-Os is a size optimization, setting this will reduce the binary file size, possibly compromising speed. I don't know if this optimization is considerable over the speed ones, but I sense that reducing the file size will also reduce the memory usage, but this is only significant if the program doesn't allocate much dynamic memory.

If you're running on a x86 machine, you can safely append -fomit-frame-pointer, because the frame-pointer is not needed on x86.

[invaderzim]

https://forums.gentoo.org/viewtopic.php?t=5717&postdays=0&postorder=asc&start=316

[puddpunk]

Yep, your much better of using -Os. Since you have small memory, you are going to see much more of a speedup than optimising with -03 (optimises code, but increases binary size, which then has to be stored in working memory).

-O3 only includes 2 extra flags than -O3, those two flags only operate in special conditions, but can sometimes act negatively for performance. -O2 is a lot more sensible and safer.

Don't know about GLIBC, I would definately use the stable version. The stable version has reliable prelinking too.

[PT_LAmb]

puddpunk, can you tell me a page that explains the few differences between -O2 and -O3, and their positive/negative impact on the system?

Thanks in advance,
Ricardo Cordeiro
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[invaderzim]

look at my post.....

[David_Escott]

definitely look at that other thread as benchmarks can tell a lot more than anything else. But I would consider using speed optimizations for low end libraries (libc and such) and then size for user end things (gnome kde etc)
your ram concerns will really kick in when you get into X and the various userland programs, but a good fast core underneath that will help too. You should also look at the cache size of your processor since cache misses will make you fall back to ram which can slow things down.

[pjp]