Messages in this thread | | | Date | Thu, 22 Dec 2005 11:58:33 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [patch 0/9] mutex subsystem, -V4 |
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On Thu, 22 Dec 2005, Ingo Molnar wrote:
> > * Nicolas Pitre <nico@cam.org> 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.
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