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

Russell King
2006-12-06T19:00:36Z

On Wed, Dec 06, 2006 at 10:56:14AM -0800, Christoph Lameter wrote:
> I'd really appreciate a cmpxchg that is generically available for
> all arches. It will allow lockless implementation for various performance
> criticial portions of the kernel.

Let's recap on cmpxchg.

For CPUs with no atomic operation other than SWP, it is not lockless.
For CPUs with load locked + store conditional, it is expensive.

I've shown in the past that a generic implementation based around ll/sc
can be cheaply implemented using cmpxchg. The reverse is *not* true.

If you want an operation for performance critical portions of the
kernel, please allow architecture maintainers the freedom to use their
best performance enhancements.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/