Re: kernel optimization options ?

Systemkennung Linux (linux@mailhost.uni-koblenz.de)
Thu, 24 Oct 1996 14:35:24 +0200 (MET DST)

> I am wondering why the kernel is as a default compiled with the -O2 and
> -fno-strength-reduced options. Why don't we use -O3 and forget the
> -fno-strength-reduced option ? The kernel gets somewhat bigger, but this
> doesn't seem te be much of a problem. Or am I missing something ?

-fno-strength-reduce is used to disable a buggy optimization in GCC 2.7.2.
Also the strength reduction doesn't work very well on CPUs with low
number of registers like Intel.

-O3 makes GCC more or less perform inline as inline can. That will
produce a quite big kernel but no equivalent speed increase. For GCC
aware code like the Linux kernel it is better to use -O2 and the inline
keyword to mark code that should be inlined. So the programmer can
balance between size and speed.

Ralf