8.6 Real world

The xv6 scheduler implements a simple scheduling policy that runs each process in turn. This policy is called round robin. Real operating systems implement more sophisticated policies that, for example, allow processes to have priorities. The idea is that a runnable high-priority process will be preferred by the scheduler over a runnable low-priority process. These policies can become complex because there are often competing goals: for example, the operating system might also want to guarantee fairness and high throughput.