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Access Method Monitor

IP.com Disclosure Number: IPCOM000081275D
Original Publication Date: 1974-May-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Winters, RM: AUTHOR

Abstract

An application program has two primary interfaces with the operating system: via a Supervisor Call Instruction (SVC) and via an access method call. Several monitoring tools are available to record the time spent in a supervisory call; however, there is no effective means at present for recording the time spent in an access method call. The transition from an application to an access method routine does not result in an interrupt; hence, the transition cannot be detected by existing interrupt driven monitors. The access method monitor described below provides a generalized technique for obtaining timing data on access method routines.

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Access Method Monitor

An application program has two primary interfaces with the operating system: via a Supervisor Call Instruction (SVC) and via an access method call. Several monitoring tools are available to record the time spent in a supervisory call; however, there is no effective means at present for recording the time spent in an access method call. The transition from an application to an access method routine does not result in an interrupt; hence, the transition cannot be detected by existing interrupt driven monitors. The access method monitor described below provides a generalized technique for obtaining timing data on access method routines.

The access method monitor is designed to provide a generalized technique for the measurement of access method routines. The access method timings are essential for the calibration of access method and application models. Interrupt driven monitors can detect transitions from an application program only if the transition results in an interrupt (SVC, program check, I/O, external interrupts). The majority of the access method calls do not result in an interrupt; hence, the transitions are not detected by the monitor.

Some interrupt driven monitors have a facility to hook points in an operating system or application program. A hook can be set by invalidating the operation code of an instruction that is to be monitored. Each attempt to execute the instruction results in a program check interrupt; which the monitor intercepts, records the data necessary to identify the event, and simulates the instruction before returning control to the normal sequence of operation.

Access method timings can be obtained from interrupt driven monitors that have a hooking facility. There are several hooking techniques currently in use; however, the technique proposed for the measurement of access methods is new and is the innovative basis for the access method monitor.

The technique takes advantage of the access method interface fields of the Data Control Block (DCB). Ea...