Suppose an application requires $N$ threads that would each use the CPU continuously until finished. All threads have to do the same amount of work. The threads don't communicate with each other and no synchronization is needed. What threading model would guarantee the highest speedup on a computer with $N$ CPUs?

one$-$to$-$one

many$-$to$-$one

two$-$level$-$model

many$-$to$-$many