Re: [PATCH] percpu: add optimized generic percpu accessors

[Tejun Heo]

Ingo Molnar wrote:
>>> and "this is preempt safe" semantics.
>> Of course.  But do any architectures actually _need_ that for a single 
>> read?
> 
> not for a read i guess - but for the other ops like add/and/or/xor.

FWIW, it prevents cross-cpu cacheline contamination.  :-)

>> Maybe.  And if so, they can interpose their arch-specific 
>> implementation.  But if the generic version is optimal for them, they 
>> wouldn't need to..
> 
> we cannot turn the generic ops into a single instruction so arch methods 
> are preferable no matter how thick or thin the generic version is. But i 
> agree that the optimization you suggest could be done.

I think the preemption protection is good to have there for, if
nothing else, documentation.

Thanks.

-- 
tejun
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