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SubjectRe: [patch 2.4 1/2] backport 2.6 x86 cpu capabilities
Mikael Pettersson wrote:
> On Fri, 08 Aug 2003 09:15:03 -0400, Jeff Garzik wrote:
>
>>>If you change NCAPINTS you also have to change the hardcoded
>>>struct offset X86_VENDOR_ID in arch/i386/kernel/head.S. Otherwise
>>>nasty stuff happen at boot since boot_cpu_data gets broken.
>>
>>
>>hmmm, reality doesn't seem to bear that out... I made the same change
>>to 2.6, without touching head.S, and life continues without "nasty
>>stuff" AFAICS.
>>
>>Do both 2.4 and 2.6 need this change? And, why didn't 2.6 break?
>
>
> 2.4.21-rc1 with NCAPINTS==6 hangs at boot in the local
> APIC timer calibration step; before that it detected a
> 0MHz bus clock and the local APIC NMI watchdog was stuck.
> Correcting head.S:X86_VENDOR_ID fixes these problems.
>
> Without correcting head.S:X86_VENDOR_ID, head.S will store
> the vendor id partly in the capabilities array. This breaks
> both the capabilities and the vendor id. I can't say why 2.6
> works, but obviously the CPU setup code has changed since 2.4.
>
> BTW, the patch below should be applied to 2.6.


Thanks for the patch, and for explaining.

Jeff



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