To summarize the thread, let me repeat something which I wrote in
personal, and expand:
(convention: iXXX refers to compilation, while XXX refers to the CPU
itslef):
1. i586 is superior to i386, in any case (of course assuming the CPU is
586 or up...).
2. i686 is superior to i586, only when multimedia instructions are
involved.
3. Under AMD, i686 requires more resources and performs slower, because
it involves extra emulation, so it may perform slower, especially if
no MMX instructions can be used.
4. Diego compared i586 with i686, not both with i386. Otherwise, his
results would be different (see 1...).
5. Since the default of most distros is i386 (including RH), most of us
understood (mistakenly) that he compared i586/i686 with i386, and
the thread went larger.
6. The reason for the "reverse" results of Diego: see 2 and 3.
7. When Gentoo mentioned the number "20%" regarding improvment, it
assumed:
a. Intel 686 or up is used (not AMD).
b. "20%" is compared to i386 (which is the default under most
distros including RH) and not i586 (under Mandrake etc.). Of
course, some apps (like the kernel) are already compiled for best
results, even under RH.
c. Under "laboratory conditions" (assuming the main bottleneck is
the CPU).
d. "20%" is not the average improvements.
Conclusion:
===========
1. If you use Intel, compile for the highest architecture you can. But
don't expect to get more than i586 would give you, because usually
there is no advantage for i686 over i586 (only in specific cases).
2. If you use AMD (or Transmeta/Geode?), compile for i586 even if you
have i686-compatible processor (e.g. Athlon etc.).
Questions:
==========
1. Does anybody have results under VMware? (I'm not sure that the
virtualization is optimal for i586/i686)
2. Has anybody experienced the Intel C Compiler? (not GCC) I heard
that its results are amazing...
--
Eli Marmor
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CTO, Founder
Netmask (El-Mar) Internet Technologies Ltd.
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