[PATCH 1/2] lib: Provide generic atomic64_t implementation

[Paul Mackerras]

Avi Kivity writes:

> An alternative implementation using 64-bit cmpxchg will recover most of 
> the costs of hashed spinlocks.  I assume most serious 32-bit 
> architectures have them?

Have a 64-bit cmpxchg, you mean?  x86 is the only one I know of, and
it already has an atomic64_t implementation using cmpxchg8b (or
whatever it's called).

My thinking is that the 32-bit non-x86 architectures will be mostly
UP, so the overhead is just an interrupt enable/restore.  Those that
are SMP I would expect to be small SMP -- mostly just 2 cpus and maybe
a few 4-way systems.

Paul.