Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an archdoesn't support it

[Christoph Lameter]

On Fri, 8 Dec 2006, David Howells wrote:

> > It is the most universal atomic instruction that I know of.
> 
> I think TAS-type things and XCHG-type things are more common.

Huh? The most popular architectures are i386 x86_64 sparc ia64 etc which 
all have one or the other form of cmpxchg (some issues with early sparc 
and i386).

And yes the xchg was the first multiprocessor instruction and therefore 
is also available on very old processors.

> In fact I think more things have LL/SC than have CMPXCHG.

LL/SC can be easily used to come up with a cmpxchg equivalent.
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