In <[EMAIL PROTECTED]>, Alexey N. Dokuchaev
wrote:
> Hi!
>
> AFAIK, Linux Mandrake has it's kernel and userland highly optimized for
> Pentium architecture. However, they have additional gcc optimization
> flags turned on by default, including -O3 and -mfast_math.
That they care for -mfast-math in the floatingpoint-free kernel shows
that they don't know what they do.
Also, both the Linux and the FreeBSD kernel suffered from unclean code
that a ANSI-C conformant compiler was allowed to break (especially
missing volatile's). Since they are fixed independetly of each other
and since these breakages change with compiler releases, you can't
make any assumptions about other kernel/compiler combinations from
experience with one combination. Also, new kernel code that people
commit is tested against -O1, so for each kernel update you had to
retest the compiler settings again until FreeBSD's official flags are
raised.
FreeBSD uses -O1 because of bugs we encountered with higher settings,
not for compile speed, in case anyone questions this. The time needed
to investigate the ability to use higher settings and redo this for
every minor compiler or assembler update is much better spent in
improving the structure of the kernel, the gain from higher -O
settings is just too small to bother. (Not that we couldn't improve
compiler testing before importing new ones...).
-O6 is like overclocking, except (much) less gain and no mineral oil
for cooling available, hence you don't even get a cooler (hehe)
looking computer.
Martin
--
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Martin Cracauer <[EMAIL PROTECTED]> http://www.cons.org/cracauer/
BSD User Group Hamburg, Germany http://www.bsdhh.org/
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