Facilitating transport mode data transfer between a channel subsystem and input/output devices

• US 8,918,542 B2
• Filed: 03/15/2013
• Issued: 12/23/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Carlson, Scott M., Casper, Daniel F., Flanagan, John R., Hathorn, Roger G., Kalos, Matthew J., Ricci, Louis W., Sittmann, Gustav E. III
• Primary Examiner(s): SUN, SCOTT C
• Application Number:
  US13/834,367
• Publication Number:
  US 20140281041A1
• Time in Patent Office: 648 Days
• Field of Search: None
• US Class Current: 710/5
• CPC Class Codes: G06F 13/122 where hardware performs an I/O function other than control of data transfer

Abstract

A computer program product is provided for performing an input/output (I/O) operation initiated by an I/O operation instruction at a host computer system configured for communication with a control unit. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing: receiving, by the control unit, a transport mode command message from a channel subsystem of the host computer system, the command message include a command for data to be transferred between the host computer system and an I/O device controlled by the control unit; and sending a command retry message to the channel subsystem, the command retry message including a request that the command message be re-sent to the control unit and a reason code indicating a reason for the request.

Claims

1. A computer program product for performing an input/output (I/O) operation initiated by an I/O operation instruction at a host computer system configured for communication with a control unit, the computer program product comprising:

a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing;

receiving, by the control unit, a transport mode command message from a channel subsystem of the host computer system, the command message include a command for data to be transferred between the host computer system and an I/O device controlled by the control unit; and

sending a command retry message to the channel subsystem, the command retry message including a request that the command message be re-sent to the control unit.

2. The computer program product of claim 1, further comprising receiving the re-sent command message and sending at least one data transfer message requesting that data be transferred to the control unit.

3. The computer program product of claim 1, wherein the command message is a transport-command information unit (IU) and the command retry message is included in a transport-response IU.

4. The computer program product of claim 3, wherein the command retry message is indicated in a device status field in the transport-response IU, the device status field including a retry status code.

5. The computer program product of claim 1, wherein the command retry message includes a reason code indicating a reason for the request.

6. The computer program product of claim 5, wherein the reason code is a transport-command-retry-reason (TCRR) code embodied in a flags field of the transport-response IU.

7. The computer program product of claim 2, further comprising controlling, by the control unit, a data transfer rate associated with the re-sent command message by at least one of pacing the sending of data transfer messages including a first data transfer message and setting a burst size of the data transfer messages including the first data transfer message.

8. The computer program product of claim 1, wherein the command message includes a write command for output data to be transferred.

9. The computer program product of claim 8, wherein the command message indicates whether first-transfer-ready is enabled, wherein:

based on first-transfer-ready being enabled, the channel subsystem is configured to transfer data to the control unit only after receiving a transfer-ready IU from the control unit; and

based on first-transfer-ready being disabled, the channel subsystem is configured to transfer data to the control unit without receiving a transfer-ready IU.

10. The computer program product of claim 9, wherein the command message indicates that first-transfer-ready is disabled, and the command retry message causes first-transfer-ready to be enabled in the channel subsystem for the I/O operation indicated in the command message.

11. The computer program product of claim 1, wherein the command message includes a transport command control block (TCCB) configured to hold a plurality of commands, and the plurality of commands are a plurality of device command words (DCW) that each is associated with an I/O command, and the TCCB is specified by a transport command word (TCW) at the channel subsystem in the host computer system for the I/O operation.

12. An apparatus for performing an input/output (I/O) operation initiated by an I/O operation instruction at a host computer system configured for communication with a control unit, comprising:

a memory having computer readable computer instructions; and

a processor for executing the computer readable instructions, the instructions including;

receiving, by the control unit, a transport mode command message from a channel subsystem of the host computer system, the command message including a command for data to be transferred between the host computer system and an I/O device controlled by the control unit; and

sending a command retry message to the channel subsystem, the command retry message including a request that the command message be re-sent to the control unit.

13. The apparatus of claim 12, wherein the command message is a transport-command information unit (IU) and the command retry message is included in a transport-response IU.

14. The apparatus of claim 13, wherein the command retry message is indicated in a device status field in the transport-response IU, the device status field including a retry status code.

15. The apparatus of claim 12, wherein the command retry message includes a reason code indicating a reason for the request.

16. The apparatus of claim 12, the instructions further comprising controlling, by the control unit, a data transfer rate associated with the re-sent command message by at least one of pacing the sending of data transfer messages including a first data transfer message and setting a burst size of the data transfer messages including the first data transfer message.

17. The apparatus of claim 12, wherein the command message includes a write command for output data to be transferred and indicates whether first-transfer-ready is enabled, wherein:

based on first-transfer-ready being enabled, the channel subsystem is configured to transfer data to the control unit only after receiving a transfer-ready IU from the control unit; and

based on first-transfer-ready being disabled, the channel subsystem is configured to transfer data to the control unit without receiving a transfer ready IU.

18. The apparatus of claim 17, wherein the command message indicates that first-transfer-ready is disabled, and the command retry message causes first-transfer-ready to be enabled in the channel subsystem for the I/O operation indicated in the command message.

19. A method of performing an input/output (I/O) operation initiated by an I/O operation instruction at a host computer system configured for communication with a control unit, the method comprising:

receiving, by the control unit, a transport mode command message from a channel subsystem of the host computer system, the command message include a command for data to be transferred between the host computer system and an I/O device controlled by the control unit; and

sending a command retry message to the channel subsystem, the command retry message including a request that the command message be re-sent to the control unit.

20. The method of claim 19, wherein the command message is a transport-command information unit (IU) and the command retry message is included in a transport-response IU.

21. The method of claim 20, wherein the command retry message is indicated in a device status field in the transport-response IU, the device status field including a retry status code.

22. The method of claim 19, wherein the command retry message includes a reason code indicating a reason for the request.

23. The method of claim 19, the method further comprising controlling, by the control unit, a data transfer rate associated with the re-sent command message by at least one of pacing the sending of data transfer messages including a first data transfer message and setting a burst size of the data transfer messages including the first data transfer message.

24. The method of claim 20, wherein the command message includes a write command for output data to be transferred and indicates whether first-transfer-ready is enabled, wherein:

based on first-transfer-ready being enabled, the channel subsystem is configured to transfer data to the control unit only after receiving a transfer-ready IU from the control unit; and

based on first-transfer-ready being disabled, the channel subsystem is configured to transfer data to the control unit without receiving a transfer ready IU.

25. The method of claim 24, wherein the command message indicates that first-transfer-ready is disabled, and the command retry message causes first-transfer-ready to be enabled in the channel subsystem for the I/O operation indicated in the command message.