In my understanding, performance is based on the value of a measure improving in one way or another. Efficiency is relative to the amount of resources required

In my understanding, performance is based on the value of a measure improving in one way or another. Efficiency is relative to the amount of resources required to achieve a similar result. To use the car example above, a car that can do 100km/h at 4L/100km is more efficient than another can than do 100km/h at 8L/100km. The point of absolute efficiency is referred to as optimum. Essentially, top performance possible with the minimum of resources possible.