Complete computer system simulation: the SimOS approach

The complexity of modern computer systems, coupled with the diverse workloads that they must support, presents a challenge to researchers and designers who need to understand a system’s behavior. We describe SimOS, a machine simulation environment designed for the efficient and accurate study of both uniprocessor and multiprocessor computer systems. SimOS simulates computer hardware in enough detail to run an entire operating system. By running a commercial operating system, SimOS provides the ability to investigate realistic workloads, which was not possible with previous simulation tools. SimOS also provides substantial flexibility in the trade-off between the speed and detail of a simulation. We employ fast simulation techniques to scan over the less interesting, time-consuming parts of a workload. To focus in on interesting sections of a workload’s execution, we employ slower, more detailed levels of simulation. SimOS’ ability to change levels of detail on-the-fly enhances its ability to study complex workloads, allowing the investigator to pay the cost of detailed simulation only when the resulting data is desired.