Why does ia64 not use fetchadd in atomic.h?

[Christoph Lameter <clameter@xxxxxxx>]

I just looked at at the asm generated by some of the use of atomic for 
statistics and saw that there were complicated compxchg constructs where I 
would have expected a simple fetchadd. Why is this?

F.e.

static __inline__ int
ia64_atomic_add (int i, atomic_t *v)
{
        __s32 old, new;
        CMPXCHG_BUGCHECK_DECL

        do {
                CMPXCHG_BUGCHECK(v);
                old = atomic_read(v);
                new = old + i;
        } while (ia64_cmpxchg(acq, v, old, new, sizeof(atomic_t)) != old);
        return new;
}

Why not

#define ia64_atomic_add(__i, __v) ia64_fetchadd(__i, &v->counter, acq)

?


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