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Storage Subsystem Single Completion Message Technique

IP.com Disclosure Number: IPCOM000034719D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Bashore, T: AUTHOR [+9]

Abstract

The Storage I/O Subsystem processes I/O requests under the control of two software Finite State Machine (FSM) programs. Communication between the FSMs is accomplished via a message passing mechanism. This is a method to reduce the number of completion messages passed to a single message and substantially reduces the overhead introduced by the message passing mechanism, improving subsystem response time and throughput. The Storage Subsystem must process a large variety of commands. Measurements of system performance indicate that a small subset of these commands (Read, Write, Skip Read, Skip Write) accounts for the majority of the requests sent to subsystem for processing.

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Storage Subsystem Single Completion Message Technique

The Storage I/O Subsystem processes I/O requests under the control of two software Finite State Machine (FSM) programs. Communication between the FSMs is accomplished via a message passing mechanism. This is a method to reduce the number of completion messages passed to a single message and substantially reduces the overhead introduced by the message passing mechanism, improving subsystem response time and throughput. The Storage Subsystem must process a large variety of commands. Measurements of system performance indicate that a small subset of these commands (Read, Write, Skip Read, Skip Write) accounts for the majority of the requests sent to subsystem for processing. A separate "fast path" is created in microcode to process these requests and to reduce the overhead of message passing, a new "single completion message" interface is hereby provided. Prior to the implementation of the single message technique, read commands were processed, as shown in Fig. 1, by the subsystem microcode. The read command is given as an example, but the write operation was processed in a similar manner. "DEV" in Fig. 1 is a Device Manager which processes requests to read and write to storage devices.

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After implementation of the single message technique, the overhead of message passing and message decode processing was reduced substantially, as shown in Fig. 2. Read and write commands are now processed in this way by the subsystem microcode:...