Re: FEATURE REQUEST: Specific Processor Optimizations on x86 Architecture

[Nick Piggin]

J.A. Magallon wrote:

> On 10.22, Joseph D. Wagner wrote:
>
> > Yes, I know you can select Pentium III, Pentium 4, Athlon, etc, under 
> > processor type when doing a 'make xconfig', but those selections do not 
> > translate into the appropriate -mcpu and -march flags.
> >
> > While the kernel on x86 architecture can be optimized in terms of generic 
> > processor specifications (i.e. i386, i486, i586, i686), the kernel can't be 
> > optimized beyond a i686.
> >
> > If you select Pentium III, the -march flag is set to i686.
> > If you select Pentium 4, the -march flag is set to i686.
> > If you select Athlon 4, the -march flag is set to i686.
> > If you select Athlon XP, the -march flag is set to i686.
> >
> > It should be that...
> >
> > If you select Pentium III, the -march flag is set to pentium3.
> > If you select Pentium 4, the -march flag is set to pentium4.
> > If you select Athlon 4, the -march flag is set to athlon-4.
> > If you select Athlon XP, the -march flag is set to athlon-xp.
> >
> > I don't want to have to hand edit the makefiles just to optimize my kernel.  
> > I think this change is simple enough to do, and would allow kernel 
> > developers the option of processor-specific optimizations in the future.
> >
> > TIA.
> >
> > Joseph D. Wagner
>
> I have sent the attached patches sometimes to the list/Marcelo, and they
> have been rejected to the moment because:
> - gcc can spit some new instructions, reorganize code and other things when
>  you jump from i686 to pentium3, for example.
> - There can be bugs both in gcc and in the kernel that can be triggered by
>  >i686 optimizations/code.
> - This is not safe for a stable kernel, it was done in 2.5, bugs appeared,
>  were corrected, and so on, 'cause this was a development kernel.

Not that I think this should go in anyway, but the only way you ever
might get it in is if you measure significant performance improvements.
I don't think you will.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/