Re: Question from Russells Spinlocks

[Parag Warudkar <kernel-stuff@comcast.net>]

Robert Love wrote:

>On Thu, 2004-12-09 at 21:15 +0000, kernel-stuff@comcast.net wrote:
>
>This part is incorrect (and horribly wrapped):
>
>  
>
>> The comment about  atomic_t - It is due to the fact that some ( IA-32 for e.g.) architectures guarantees atomicity of integer operations for only 24 bits. So you could possibly manipulate only 24 out of the 32 bits atomically - that's the hardware guarantee. The comments reflect this fact. (Pointers are 32bits on IA32 so it applies to pointer as well.)
>>    
>>
>
>The reason for the 24-bit limit on atomic_t is because SPARC32's
>implementation of atomic operations was limited to 24-bits per atomic
>integer, because the architecture provides very minimal atomic support,
>we had to embed a byte-sized lock in the word.  This limited SPARC32's
>atomic integer to 24 usable bits.  The other architectures can, of
>course, hold the full 32-bits but to be compatible code must assume the
>24-bit limit.
>
>Although this was fixed recently in 2.6 so it actually no longer
>applies.
>  
>
Yes - I understand it better now. Thanks!

Parag