To build such a scheduler, in this chapter we will describe the basic algorithms behind a multi-level feedback queue; although the specifics of many implemented MLFQs differ, most approaches are similar“An Analysis of Decay-Usage Scheduling in Multiprocessors” by D.H.J. Epema. SIG- METRICS ’95. A nice paper on the state of the art of scheduling back in the mid-1990s, including a good overview of the basic approach behind decay-usage schedulers..

Priority-based rules

In our treatment, the MLFQ has a number of distinct queues, each assigned a different priority level. At any given time, a job that is ready to run is in a single queue. MLFQ uses priorities to decide which job should run at a given time: a job with higher priority (i.e., a job on a higher queue) is chosen to run. Of course, more than one job may be in a given queue and thus have the same priority. In this case, we will just use round-robin scheduling among those jobs.

Thus, we arrive at the first two basic rules for MLFQ:

Rule 1: If $Priority(A) >$ ...

MLFQ: Basic Rules