Browse Prior Art Database

Tunable NOOP Lookahead Algorithm

IP.com Disclosure Number: IPCOM000034734D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 4 page(s) / 91K

Publishing Venue

IBM

Related People

Blades, JA: AUTHOR [+3]

Abstract

An algorithm enhances the performance of an I/O Processor (IOP), implementing a System/370 I/O Architecture to Intelligent Peripheral Interface (IPI-3) I/O control interface, for those operations defined by Channel Command Word (CCW) chains ending in NOOP CCWs. Certain applications commonly place either a NOOP CCW or a TIC-to-TIC+8 - NOOP CCW group at the end of the I/O CCW Chains, thus making these types of operation chains critical to overall system performance. Performance of these CCW chain types is impacted due to additional logical level (Image Omitted) control at the IPI-3 device interface, as well as overhead for the fetch and validation of the additional CCWs.

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Tunable NOOP Lookahead Algorithm

An algorithm enhances the performance of an I/O Processor (IOP), implementing a System/370 I/O Architecture to Intelligent Peripheral Interface (IPI-3) I/O control interface, for those operations defined by Channel Command Word (CCW) chains ending in NOOP CCWs. Certain applications commonly place either a NOOP CCW or a TIC-to-TIC+8 - NOOP CCW group at the end of the I/O CCW Chains, thus making these types of operation chains critical to overall system performance. Performance of these CCW chain types is impacted due to additional logical level

(Image Omitted)

control at the IPI-3 device interface, as well as overhead for the fetch and validation of the additional CCWs. This algorithm reduces the average response time of such an operation to a level equivalent to that of operations defined by CCW chains without the additional CCW(s) through efficient processing of the CCW chain and reduction of device interface interaction.

(Image Omitted)

NOOP Lookahead processing is only invoked when a threshold percentage of the CCW Chains end with NOOPs, as shown in Fig. 1. At the completion of processing for a LOC CCW 10, which basically defines an IPI-3 operation, a check for number of LOC CCWs is made (20). If enough LOC CCWs have been processed, i.e., a window of operations, the ratio of CCW chains ending with NOOPs to other CCW chains is calculated (30). If the End-of-Chain NOOP ratio for the current workload exceeds the threshold ratio (40), NOOP Lookahead is enabled (50); otherwise, it is disabled (60). This selects the method for processing CCWs which is most appropriate for the workload. Note that the ability to tune the algorithm lies in this section. The threshold of LOC CCWs to be processed before checking the workload ratio controls how rapidly the algorithm responds to changes in the characteristics of th...