Re: [PATCH 13/15] x86: add cmpxchg_flag() variant

[H. Peter Anvin]

On 08/24/2011 12:27 PM, Christoph Lameter wrote:
> 
> Indeed for sete the size of the argument does not matter. Look at
> percpu_cmpxchg_double() and cmpxchg_double() in arch/x86/include for some
> of the functions I wrote. The sete is used to avoid the double word
> comparisons that would otherwise have been necessary.
> 
> But still the solution with the flags would save another instruction and
> the generated code would not be as ugly. For not only do you have an
> additional sete you will then also have to check the result again. This
> means at least two additional instruction.
> 

The sete is actually more expensive than the compare for the single-word
case.  The double-word case is a different matter.

	-hpa


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