Re: RFC: [2.6 patch] better i386 CPU selection

Mikael Pettersson
2003-09-07T21:48:34Z

On Sun, 7 Sep 2003 19:51:50 +0200, Adrian Bunk wrote:
>> >In 2.6 selecting M486 means that only the 486 is supported.
>>
>> Can you prove your claim about 2.6?
>>
>> There is to the best of my knowledge nothing in 2.6.0-test4
>> that prevents a kernel compiled for CPU type N from working
>> with CPU types >N. Just to prove it, I built a CONFIG_M486
>> 2.6.0-test4 and booted it w/o problems on P4, PIII, and K6-III.
>
>Look at X86_L1_CACHE_SHIFT in arch/i386/Kconfig.

I have. All it does is change how much space the kernel
allocates to spinlocks and some other structures. This is
merely an optimisation primarily for SMP. This does not
prevent code from executing correctly on CPUs having a
different actual L1 cache line size.

>> (In case 2 configure for PIII and use that on PIII and P4.)
>>
>> Maybe I'm missing something but I don't see any problem here.
>
>In current 2.6 this is only legal with X86_GENERIC enabled.

No. You're over-interpreting X86_GENERIC. All it does is
change some optimisation defaults. It is not required for
correctness.

/Mikael