Matsushita Electric Industrial Co., Ltd.

Thirumale N Niranjan

Ibrahim Mostafa Kamel

Shahram Ghandeharizadeh

Walid G Aref

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.

Real time scheduling of prioritized disk requests

The disk scheduling system supports the processing of simultaneous storage device read and write requests in a video server environment, thereby supporting both video-on-demand and non-linear editing applications. Read requests are the result of movie viewing, while write requests are the result of video clip editing or movie authoring procedures. Due to real-time demands of movie viewing, read requests have to be fulfilled within certain deadlines, otherwise they are considered lost. Since the data to be written into the storage device is stored in main memory buffers (or write buffers), write requests can be postponed until critical read requests are processed. However, write requests still have to be proceeded within reasonable delays and without the possibility of indefinite postponement. This is due to the physical constraint of the limited size of the main memory buffers. The new process treats both read and write requests in a homogenous manner in order to ensure that the deadlines are met and avoids indefinite postponement and large buffer sized in the case of storage device writes utilizing a single queue of requests.

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Pittsburgh, PA, United States of America

Thirumale N Niranjan