Messages in this thread | | | Date | Fri, 24 Oct 2003 09:24:01 +1000 | From | Nick Piggin <> | Subject | Re: FEATURE REQUEST: Specific Processor Optimizations on x86 Architecture |
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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.
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