On Thu, 22 Dec 2005, Ingo Molnar wrote:
>
> * Nicolas Pitre <[email protected]> wrote:
>
> > > i'm curious, how would this ARMv6 solution look like, and what would be
> > > the advantages over the atomic swap based variant?
> >
> > On ARMv6 (which can be SMP) the atomic swap instruction is much more
> > costly than on former ARM versions. It however has ll/sc instructions
> > which allows it to implement a true atomic decrement, and the lock
> > fast path would look like: [...]
>
> but couldnt you implement atomic_dec_return() with the ll/sc
> instructions? Something like:
NO. My first example was atomic_dec_return based. The second is
lighter and fulfill the semantics of arch_mutex_fast_lock() but is not a
common atomic primitive.
Nicolas
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