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SubjectRe: [cpuops cmpxchg double V1 1/4] Generic support for this_cpu_cmpxchg_double
On 12/21/2010 02:36 PM, Christoph Lameter wrote:
> On Sat, 18 Dec 2010, Tejun Heo wrote:
>
>> pointers from the beginning. Anyways, that's too late, so is it
>> completely impossible to make cmpxchg_double's take a scalar value?
>> It can take the pointer all the same, no?
>
> It could take a scalar value like the others but we are then not operating
> on the scalar alone but also on the following field.
>

I'm a bit confused on this one. The standard cmpxchg() takes a scalar
and a pointer, and returns a scalar. The equivalent for the "double"
variety would be to return a compound object, basically:

struct double_ulong {
unsigned long v[2];
};
... which can be returned in registers on both i386 and x86-64.

It's a bit clumsy from a type perspective, but I'm not sure that that is
a bad thing. Doing too much type genericity has caused us problems in
the past.

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.



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