Closed loop is the practical methodology applied at every tier in the top-down process. It is a rigorous cycle of activity whose sequence of steps is strictly followed at every layer: 1. Gather performance data This tight loop of activity continues until you are satisfied that all the optimization that can be wrought from one level has been performed. You then move to the next lower level and repeat the closed loop — again until you’ve extracted the available performance benefits or you reach the performance target you need.
2. Analyze data and identify issues
3. Generate an alternative
4. Implement the enhancement
5. Test new solutions, and return to step 1
— Intel Optimization Best Practices: No Magic, Just Discipline and Good Tools
