Real time scheduling of prioritized disk requests

摘要

A single queue is utilized for scheduling of prioritized requests having specific deadlines in which to be serviced. New requests are initially inserted into the single queue based upon optimal SCAN order. Once the new request is inserted, the deadlines of all the requests in the queue are checked in order to insure each request deadline is met. In the event a deadline violation is identified, the queue is reorganized by identifying the lowest priority request currently to be processed prior to the request with the deadline violation. If more than one request with the lowest priority exists, the lowest priority request with the greatest deadline slack is selected. Ultimately, the selected request is moved to the tail of the queue, or removed from the queue and considered lost if its deadline is violated with a queue tail placement. This process is repeated until the queue is in a state with no deadline violations.