Re: [RFC] New locking primitive for 2.5

[Jeff Garzik <jgarzik@mandrakesoft.com>]

Linus Torvalds wrote:
> 
> On Fri, 8 Feb 2002, Ingo Molnar wrote:
> >
> > and regarding the reintroduction of BKL, *please* do not just use a global
> > locks around such pieces of code, lock bouncing sucks on SMP, even if
> > there is no overhead.
> 
> I'd suggest not having a lock at all, but instead add two functions: one
> to read a 64-bit value atomically, the other to write it atomically (and
> they'd be atomic only wrt each other, no memory barriers etc implied).
> 
> On 64-bit architectures that's just a direct dereference, and even on x86
> it's just a "cmpxchg8b".

Are there architectures out there that absolutely must implement this
with a spinlock?  Your suggested API of functions to read/write 64-bit
values atomically would work for such a case, but still I am just
curious.

	Jeff


-- 
Jeff Garzik      | "I went through my candy like hot oatmeal
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