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

Paul Mackerras
2009-06-14T12:21:42Z

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.