If I'm understanding correctly, you measured pthread_lock as having about twice the overhead of a spin lock. As discussed elsethread, this is expected on x86 as a spinlock only needs an expensive CAS on lock and a cheap store on unlock, while a pthread_lock needs a CAS on both lock and unlock.
Actually, in the micro benchmark the mutexes were five times slower than the spinlocks. In a real hpc application I reduced the runtime by 30-40% just by replacing them with spinlocks.
