Browse Prior Art Database

I/O Off-Level Control in a Virtual Resource Manager

IP.com Disclosure Number: IPCOM000062215D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Greenberg, MS: AUTHOR

Abstract

By providing an I/O off-level control in a Virtual Resource Manager (VRM), the Second Level Interrupt Handler (SLIH) can reduce latency for all equal and lower priority classes. Normally, a SLIH runs to completion in the VRM, preventing all I/O devices from interrupting unless they are of a higher priority class. It is possible to work around this by designing the device driver to be a SLIH and a device manager process. This approach, however, adds significant path length (an additional level of queueing) which could result in performance degradation and complexity in debugging the code. The solution to this problem is to provide an I/O off-level control in the VRM.

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I/O Off-Level Control in a Virtual Resource Manager

By providing an I/O off-level control in a Virtual Resource Manager (VRM), the Second Level Interrupt Handler (SLIH) can reduce latency for all equal and lower priority classes. Normally, a SLIH runs to completion in the VRM, preventing all I/O devices from interrupting unless they are of a higher priority class. It is possible to work around this by designing the device driver to be a SLIH and a device manager process. This approach, however, adds significant path length (an additional level of queueing) which could result in performance degradation and complexity in debugging the code. The solution to this problem is to provide an I/O off-level control in the VRM. This approach allows the SLIH to request lower level processing for the device so that additional interrupts can be processed while the lower level processing is running. This lower level processing (off-level routine) runs in the same environment as the SLIH and not like a VRM process. This technique reduces Asynch overrun problems. Thus, transmit interrupts as well as clerical system interfaces (DEQUE, ENQUE, etc.) can be executed and not hold off the receive interrupt. An additional problem occurred in that off-level processing could be scheduled for devices of several priorities. This was solved by having two levels of off-level priorities. The higher priority is for class 0 devices (highest priority), and the lower priority is for classes 1 thro...