Re: [PATCH 1/5] bitops: add generic implementation of ext2 atomicbitops by test_and_{set,clear}_bit

[Akinobu Mita]

2010/10/11 Arnd Bergmann <arnd@xxxxxxxx>:
> On Sunday 10 October 2010 17:07:26 Akinobu Mita wrote:
>> Some architectures use spinlock to implement it
>> (asm-generic/bitops/ext2-atomic.h). Most other architectures use
>> test_and_set_bit() and test_and_clear_bit() as this patch shows.
>>
>> Why are there two implementations? test_and_{set,clear}_bit() are more
>> costly operations than spinlock for some architectures?
>
> I would guess that is only true on architectures that implement all atomics
> using a hashed spinlock like cris, sparc32 or parisc. This way the user
> can decide which spinlock to use rather than have the arch code calculate
> a hash on the pointer.

Thanks. It looks quite right.

> This is an ext2 specific micro-optimization that I don't think makes
> sense in the generic le bitops code.

OK, I'll only rename ext2 non-atomic bitops to le bitops and
keep ext2 atomic bitops for now.
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