Re: [PATCH] [2.4] [2.5] [i386] Add support for GCC 3.1 -march=pentium{-mmx,3,4}

Ruth Ivimey-Cook
2002-05-25T23:53:44Z

On Sun, 26 May 2002, Luigi Genoni wrote:
>On Sun, 26 May 2002, Dave Jones wrote:
>> On Sun, May 26, 2002 at 01:37:39AM +0200, J.A. Magallon wrote:
>> > Could you also split
>> > Pentium-Pro/Celeron/Pentium-II CONFIG_M686
>> > into
>> > Pentium-Pro CONFIG_M686
>> > Pentium-II/Celeron CONFIG_MPENTIUMII
>> There are also a few extra Athlon targets iirc. athlon-xp and the like,
>> which I'm not sure the purpose of. Some gcc know-all want to clue me in
>> to what these offer over -march=athlon ?
>>
>I do not know about the gcc options, but Athlon XP/MP has sse instruction,
>while tbird has not, so it could be relate to this.
>
>> > BTW, I think an option to enable -mmmx would also be useful. Nothing more,
>> > because afaik sse is only floating point.

For the CONFIG_<<cputype>> options, is it only gcc compiler-type settings that
are affected? I thought the assembly parts of the kernel were also switched on
occasion.

I was wondering whether anyone has checked that these assembly snippets were
decently optimal for the cpu type selected...

>> Another interesting recently-added option which may be worth
>> benchmarking on modern CPUs is the prefetch-loops option.
>> In a lot of cases, the kernel 'knows better' and is adding the

Be careful about 'knowing better' than compilers. I really don't want to start
a flamefest, but modern compilers are very good at doing all sorts of
optimisations, and hand-coded 'optimisations' can _sometimes_ actually hurt
performance over the unadorned version of the code. It is sensible to prove
that the source-level optimisation helps, and then to mark it as such, so as
compilers change it can be reviewed.

Regards,

Ruth

--
Ruth Ivimey-Cook
Software engineer and technical writer.