Browse Prior Art Database

Automatic Response Packet Transfer Technique

IP.com Disclosure Number: IPCOM000034537D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Fasig, JL: AUTHOR [+5]

Abstract

This technique improves the performance of a Storage Subsystem by eliminating packet attention message processing and queueing delays. Originally, HWC provided the functions of data transfer and response packet transfer as two separate functions, each requiring a separate HWC procedure call. In normal operation, HWC would send one message to Device Manager when the data transfer was completed, and send another message when the device raised attention and answered the packet attention poll. The Device Manager dequeued messages from its mailbox, and when it received the packet poll message, it would call HWC to request the response packet transfer.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 55% of the total text.

Page 1 of 2

Automatic Response Packet Transfer Technique

This technique improves the performance of a Storage Subsystem by eliminating packet attention message processing and queueing delays. Originally, HWC provided the functions of data transfer and response packet transfer as two separate functions, each requiring a separate HWC procedure call. In normal operation, HWC would send one message to Device Manager when the data transfer was completed, and send another message when the device raised attention and answered the packet attention poll. The Device Manager dequeued messages from its mailbox, and when it received the packet poll message, it would call HWC to request the response packet transfer. The time required to send, receive, and process the packet transfer could be several milliseconds due to queueing delays if there were already other messages in the Device Manager mailbox. This delay lowered the Storage Subsystem's performance and affected all the devices which attach to the hardware, but it was quite noticeable when attaching DASD devices with multiple facilities because these devices refuse to accept new commands for any facility until the current response packet has been transferred. The net effect of this refusal was that all incoming DASD requests incurred this packet poll delay, not just the operation responsible for the response packet. This delay was also particularily detrimental when attaching tape devices because the delay added to the code path tim...