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Queueing Discipline for Hard File Adapters

IP.com Disclosure Number: IPCOM000038588D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Fogg, RG: AUTHOR [+6]

Abstract

A queueing discipline for hard files is described which allows data sets on hard files which consist of numerous contiguous data blocks to be efficiently accessed. It is most applicable to a system containing several hard files controlled by a single adapter card. The queue discipline allows the adapter card to employ a very simple scheduling algorithm, yet it provides many of the benefits of much more complex and expensive queueing schemes. The scheduling algorithm is a modification of a Round Robin (RR) job execution order, with each job of the RR consisting of a first-in, first-out (FIFO) queue of jobs. The algorithm is outlined below for a system containing n hard files.

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Queueing Discipline for Hard File Adapters

A queueing discipline for hard files is described which allows data sets on hard files which consist of numerous contiguous data blocks to be efficiently accessed. It is most applicable to a system containing several hard files controlled by a single adapter card.

The queue discipline allows the adapter card to employ a very simple scheduling algorithm, yet it provides many of the benefits of much more complex and expensive queueing schemes. The scheduling algorithm is a modification of a Round Robin (RR) job execution order, with each job of the RR consisting of a first-in, first-out (FIFO) queue of jobs. The algorithm is outlined below for a system containing n hard files. I=1

START While (queue for file i empty) DO i=i+1 (modulo n) ENDWHILE Decode command at top of FIFO queue for file i

IF (no seek required OR seek part of command is complete)

THEN

Transfer data and complete task

ELSE

Initiate the seek operation

i = i + 1 (modulo n)

END IF

GO TO START Each file queue can be limited to m commands to allow an even simpler adapter scheduling algorithm and to free the microprocessor on the adapter card from accepting large numbers of new host commands while simultaneously managing the file interfaces. Because of its simplicity, this queueing discipline may be implemented in microcode residing in a read-only memory (ROM) on the adapter card and executed by a low-cost processor. The same processor could also be used to accept new commands from the host and to pass status to the host after command completion. This queueing discipline is applicable to a UNIX* operating system environment in which large data sets consist of numerous (2K Byte) smaller data blo...