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

Russell King
2006-12-08T19:44:12Z

On Fri, Dec 08, 2006 at 11:37:45AM -0800, Linus Torvalds wrote:
>
>
> On Fri, 8 Dec 2006, Russell King wrote:
> >
> > I utterly disagree. I could code atomic_add() as:
>
> Sure. And Alpha could do that too. If you write the C code a specific way,
> you can make it work. That does NOT mean that you can expose it widely as
> a portable interface - it's still just a very _nonportable_ interface that
> you use internally within one architecture to implement other interfaces.

However, nothing stops you wrapping the non-portable nature of ll/sc up
into the store part though.

If you can efficiently implement cmpxchg inside an ll/sc based portable
interface (yes you can) and you can implement problematical ll/sc
structures inside a cmpxchg() interface, you can do it either way around.
Only one way doesn't penalise broken ll/sc based implementations though.

That is the essence of my argument.

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