Decide what you want to measure. In some cases, you just want to see how quickly you can do something. For example, you might have competing algorithms to assess, or you just want to see how fast you can make something run. For example, a file-based compiler might compile 500K lines of code per minute on a 400 MHz x86 system. For interactive systems, the focus is both response time and throughput .
Response time is how long it takes from start to finish for a single request.
For example, a web server might handle 200K requests per hour with sub-second response time. When you're testing, you're well advised to measure system load as well. This makes it easier to predict performance on different systems. Without the load measure, it would be hard to know this. Give yourself a deadline.