# Patent

## Title
Facilitating input/output processing by using transport control words to reduce input/output communications

## Abstract

Input/output processing is facilitated by reducing communications between input/output communications adapters and control units during input/output processing. The number of exchanges and sequences between an input/output communications adapter and control unit is reduced by sending a plurality of commands from the adapter to the control unit as a single entity for execution by the control unit. The control unit executes the commands and provides the data, if any, in one sequence. The control unit relieves the adapter of the responsibility of tracking state of the individual commands and is able to calculate precise measurement data relating to execution of the commands.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application contains subject matter which is related to the subject matter of the following application, assigned to the same assignee as this application and hereby incorporated herein by reference in its entirety:
“FACILITATING ACCESS TO STATUS AND MEASUREMENT DATA ASSOCIATED WITH INPUT/OUTPUT PROCESSING,” Casper et al., U.S. Ser. No. 11/548,093, filed Oct. 10, 2006.
TECHNICAL FIELD
This invention relates, in general, to input/output processing, and in particular, to using a transport control word to reduce input/output communications during input/output processing.
BACKGROUND OF THE INVENTION
Input/output (I/O) operations are used to transfer data between memory and input/output devices of a processing environment. Specifically, data is written from memory to one or more input/output devices, and data is read from one or more input/output devices to memory by executing input/output operations.
To facilitate processing of input/output operations, an input/output subsystem of the processing environment is employed. The input/output subsystem is coupled to main memory and the input/output devices of the processing environment and directs the flow of information between memory and the input/output devices. One example of an input/output subsystem is a channel subsystem. The channel subsystem uses channel paths as communications media. Each channel path includes a channel coupled to a control unit, the control unit being further coupled to one or more input/output devices.
The channel subsystem employs channel command words to transfer data between the input/output devices and memory. A channel command word specifies the command to be executed, and for commands initiating certain I/O operations, it designates the memory area associated with the operation, the action to be taken whenever transfer to or from the area is completed, and other options.
During input/output processing, a list of channel command words is fetched from memory by a channel. The channel parses each command from the list of channel command words and forwards a number of the commands, each command in it's own entity, to a control unit coupled to the channel. The control unit then processes the commands. The channel tracks the state of each command and controls when the next set of commands are to be sent to the control unit for processing. The channel ensures that each command is sent to the control unit in it's own entity.
SUMMARY OF THE INVENTION
Enhancements to the above processing of commands are needed. For example, a need exists for a capability that enables multiple commands to be sent to the control unit as a single entity. A further need exists for a capability that eliminates the need for the channel to track the status of the individual commands being executed by the control unit. A need exists for a capability that reduces communication (e.g., exchanges and sequences) between the channel and control unit during I/O processing.
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a method of facilitating input/output processing of a processing environment. The method, includes, for instance, obtaining by an input/output communications adapter of the processing environment a transport control word, said transport control word specifying a location in memory of the processing environment that includes a plurality of input/output commands to be executed; forwarding from the input/output communications adapter to a control unit of the processing environment the plurality of input/output commands as one entity; and executing by the control unit the plurality of input/output commands to perform one or more input/output operations, wherein the executing is performed absent a tracking by the input/output communications adapter of state relative to the individual input/output commands of the plurality of input/output commands being executed by the control unit.
System and computer program products corresponding to the above-summarized method are also described and claimed herein.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.



BRIEF DESCRIPTION OF THE DRAWINGS
One or more aspects of the present invention are particularly pointed out and distinctly claimed as examples in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 depicts one embodiment of a processing environment incorporating and using one or more aspects of the present invention;
FIG. 2a depicts one example of a channel command word;
FIG. 2b depicts one example of a channel command word channel program;
FIG. 3 depicts one embodiment of a link protocol used in communicating between the channel and control unit to execute the channel command word channel program of FIG. 2b; 
FIG. 4 depicts one embodiment of a transport control word channel program, in accordance with an aspect of the present invention;
FIG. 5 depicts one embodiment of a link protocol used to communicate between a channel and control unit to execute the transport control word channel program of FIG. 4, in accordance with an aspect of the present invention;
FIG. 6 depicts one embodiment of a link protocol used to communicate between a channel and control unit in order to execute four read commands of a channel command word channel program;
FIG. 7 depicts one embodiment of a link protocol used to communicate between a channel and control unit to process the four read commands of a transport control word channel program, in accordance with an aspect of the present invention;
FIG. 8 depicts one embodiment of a transport control word used in accordance with an aspect of the present invention;
FIG. 9 depicts one embodiment of a channel command word descriptor specified by the transport control word of FIG. 8 and used in accordance with an aspect of the present invention;
FIG. 10 depicts one embodiment of ending status specified by the transport control word of FIG. 8 and used in accordance with an aspect of the present invention;
FIG. 11 depicts one embodiment of response information received for a channel command word channel program;
FIG. 12 depicts one embodiment of response information received for a transport control word channel program, in accordance with an aspect of the present invention; and
FIG. 13 depicts one embodiment of a computer program product incorporating one or more aspects of the present invention.



BEST MODE FOR CARRYING OUT THE INVENTION
In accordance with an aspect of the present invention, input/output processing is facilitated by reducing communications between components of a processing environment used to perform the input/output processing. For instance, the number of exchanges and sequences between an input/output (I/O) communications adapter, such as a channel, and a control unit is reduced. This is accomplished by sending a plurality of commands from the I/O communications adapter to the control unit as a single entity for execution by the control unit, and by the control unit sending the data resulting from the commands, if any, as a single entity.
The plurality of commands are included in a descriptor, referred to herein as a channel command word descriptor, an address of which is specified in a transport control word. The transport control word is sent from the operating system or other application to the I/O communications adapter, which in turn forwards the descriptor to the control unit for processing. The control unit processes each of the commands absent a tracking of status relative to those individual commands by the I/O communications adapter.
One example of a processing environment incorporating and using one or more aspects of the present invention is described with reference to FIG. 1. Processing environment 100 includes, for instance, a main memory 102, one or more central processing units (CPU) 104, a storage control element 106, a channel subsystem 108, one or more control units 110 and one or more input/output (I/O) devices 112, each of which is described below.
Main memory 102 stores data and programs, which are input from input devices 112. Main memory 102 is directly addressable and provides for high-speed processing of data by central processing units 104 and channel subsystem 108.
Central processing unit 104 is the controlling center of environment 100. It contains the sequencing and processing facilities for instruction execution, interruption action, timing functions, initial program loading, and other machine-related functions. Central processing unit 104 is coupled to storage control element 106 via a connection 114, such as a bidirectional or unidirectional bus.
Storage control element 106 is coupled to main memory 102 via a connection 116, such as a bus; to central processing units 104 via connection 114; and to channel subsystem 108 via a connection 118. Storage control element 106 controls, for example, the queuing and execution of requests made by CPU 104 and channel subsystem 108.
Channel subsystem 108 is coupled to storage control element 106, as described above, and to each of the control units via a connection 120, such as a serial link. Channel subsystem 108 directs the flow of information between input/output devices 112 and main memory 102. It relieves the central processing units of the task of communicating directly with the input/output devices and permits data processing to proceed concurrently with input/output processing. The channel subsystem uses one or more channel paths 122 as the communication links in managing the flow of information to or from input/output devices 112. As a part of the input/output processing, channel subsystem 108 also performs the path-management functions of testing for channel path availability, selecting an available channel path and initiating execution of the operation with the input/output devices.
Each channel path 122 includes a channel 124 (channels are located within the channel subsystem, in one example, as shown in FIG. 1), one or more control units 110 one or more connections 120. In another example, it is also possible to have one or more dynamic switches as part of the channel path. A dynamic switch is coupled to a channel and a control unit and provides the capability of physically interconnecting any two links that are attached to the switch.
Also located within channel subsystem 108 are subchannels (not shown). One subchannel is provided for and dedicated to each input/output device accessible to a program through the channel subsystem. A subchannel (e.g., a data structure, such as a table) provides the logical appearance of a device to the program. Each subchannel provides information concerning the associated input/output device 112 and its attachment to channel subsystem 108. The subchannel also provides information concerning input/output operations and other functions involving the associated input/output device. The subchannel is the means by which channel subsystem 108 provides information about associated input/output devices 112 to central processing units 104, which obtain this information by executing input/output instructions.
Channel subsystem 108 is coupled to one or more control units 110. Each control unit provides the logic to operate and control one or more input/output devices and adapts, through the use of common facilities, the characteristics of each input/output device to the link interface provided by the channel. The common facilities provide for the execution of input/output operations, indications concerning the status of the input/output device and control unit, control of the timing of data transfers over the channel path and certain levels of input/output device control.
Each control unit 110 is attached via a connection 126 (e.g., a bus) to one or more input/output devices 112. Input/output devices 112 receive information or store information in main memory 102 and/or other memory. Examples of input/output devices include card readers and punches, magnetic tape units, direct access storage devices, displays, keyboards, printers, pointing devices, teleprocessing devices, communication controllers and sensor based equipment, to name a few.
One or more of the above components of the processing environment are further described in “IBM® z/Architecture Principles of Operation,” Publication No. SA22-7832-04, 5th Edition, September 2005; U.S. Pat. No. 5,461,721 entitled “System For Transferring Data Between I/O Devices And Main Or Expanded Storage Under Dynamic Control Of Independent Indirect Address Words (IDAWS),” Cormier et al., issued Oct. 24, 1995; and U.S. Pat. No. 5,526,484 entitled “Method And System For Pipelining The Processing Of Channel Command Words,” Casper et al., issued Jun. 11, 1996, each of which is hereby incorporated herein by reference in its entirety. IBM is a registered trademark of International Business Machines Corporation, Armonk, N.Y., USA. Other names used herein may be registered trademarks, trademarks or product names of International Business Machines Corporation or other companies.
In one embodiment, to transfer data between devices 112 and memory 102, channel command words are used. A channel command word specifies the command to be executed, and includes other fields to control processing. One example of a channel command word is described with reference to FIG. 2a. A channel command word 200 includes, for instance, a command code 202 specifying the command to be executed (e.g., read, read backward, control, sense and write); a plurality of flags 204 used to control the I/O operation; for commands that specify the transfer of data, a count field 206 that specifies the number of bytes in the storage area designated by the CCW to be transferred; and a data address 208 that points to a location in main memory that includes data, when direct addressing is employed, or to a list (e.g., contiguous list) of modified indirect data address words (MIDAWs) to be processed, when modified indirect data addressing is employed. Modified indirect addressing is further described in U.S. application Ser. No. 11/464,613, entitled “Flexibly Controlling The Transfer Of Data Between Input/Output Devices And Memory,” Brice et al., filed Aug. 15, 2006, which is hereby incorporated herein by reference in its entirety.
One or more channel command words (CCWs) arranged for sequential execution form a channel program, referred to herein as a CCW channel program. The CCW channel program is set up by, for instance, the operating system, or other software. The software sets up the CCWs and obtains the addresses of memory assigned to the channel program. An example of a CCW channel program is described with reference to FIG. 2b. A CCW channel program 210 includes, for instance, a define extent channel command word (CCW) 212 that has a pointer 214 to a location in memory of define extent data 216 to be used with the define extent command. In this example, a transfer in channel (TIC) 218 follows the define extent command that refers the channel program to another area in memory (e.g., an application area) that includes one or more other CCWs, such as a locate record 217 that has a pointer 219 to locate record data 220, and one or more read CCWs 221. Each read CCW 220 has a pointer 222 to a data area 224. The data area includes an address to directly access the data or a list of data address words (e.g., MIDAWs or IDAWs) to indirectly access the data. Further, CCW channel program 210 includes a predetermined area in the channel subsystem defined by the device address called the subchannel for status 226 resulting from execution of the CCW channel program.
The processing of a CCW channel program is described with reference to FIG. 3, as well as with reference to FIG. 2b. In particular, FIG. 3 shows an example of the various exchanges and sequences that occur between a channel and a control unit when a CCW channel program is executing. The link protocol used for the communications is FICON (Fibre Connectivity), in this example. Information regarding FICON is described in “Fibre Channel Single Byte Command Code Sets-2 Mapping Protocol (FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003), which is hereby incorporated herein by reference in its entirety.
Referring to FIG. 3, a channel 300 opens an exchange with a control unit 302 and sends a define extent command and data associated therewith 304 to control unit 302. The command is fetched from define extent CCW 212 (FIG. 2b) and the data is obtained from define extent data area 216. The channel uses TIC 218 to locate the locate record CCW and the read CCW. It fetches the locate record command 305 (FIG. 3) from the locate record CCW 217 (FIG. 2B) and obtains the data from locate record data 220. The read command 306 (FIG. 3) is fetched from read CCW 221 (FIG. 2B). Each is sent to the control unit.
The control unit opens an exchange 308 with the channel, in response to the open exchange of the channel. This can occur before or after locate command 305 and/or read command 306. Along with the open exchange, a response (CMR) is forwarded to the channel. The CMR provides an indication to the channel that the control unit is active and operating.
The control unit sends the requested data 310 to the channel. Additionally, the control unit provides the status to the channel and closes the exchange 312. In response thereto, the channel stores the data, examines the status and closes the exchange 314, which indicates to the control unit that the status has been received.
The processing of the above CCW channel program to read 4k of data requires two exchanges to be opened and closed and seven sequences. In accordance with an aspect of the present invention, the number of exchanges and sequences between the channel and control unit is reduced by collapsing multiple commands of the channel program into one command word, referred to as a transport control word (TCW). Specifically, the transport control word points to a channel command word descriptor (CCWD) that includes the multiple commands. The TCW is executed by the host channel and is not sent or seen by the control unit.
One example of a channel program to read 4k of data, as in FIG. 2b, but includes a transport control word, instead of separate individual channel command words, is described with reference to FIG. 4. As shown, a channel program 400, referred to herein as a TCW channel program, includes a transport control word 402 specifying a location in memory of a channel command word descriptor (CCWD) 404, as well as a location in memory of a data area 406 or a MIDAL 410 (i.e., a list of MIDAWs) that points to data area 406, and a status area 408. Transport control words, channel command word descriptors and status are described in further detail below.
The processing of a TCW channel program is described with reference to FIG. 5. The link protocol used for these communications is, for instance, the fibre channel protocol (FCP). In particular, the three phases of the FCP link protocol are used, allowing host bus adapters to be used that support FCP to support data transfers controlled by CCWs. FCP and its phases are described further in “Information Technology—Fibre Channel Protocol for SCSI, Third Version (FCP-3),” T10 Project 1560-D, Revision 4, Sep. 13, 2005, which is hereby incorporated herein by reference in its entirety.
Referring to FIG. 5, a channel 500 opens an exchange with a control unit 502 and sends the channel command word descriptor 504 to the control unit. In one example the CCWD and sequence initiative are transferred to the control unit in a FCP command, referred to as FCP_CMND IU. The control unit executes the multiple commands of the channel command word descriptor (e.g., define extent command, locate record command, read command) and forwards the data 506 to the channel via, for instance, a FCP_Data IU. It also provides status and closes the exchange 508. As one example, final status is sent in a FCP status frame that has a bit active in, for instance, byte 10 or 11 of the FCP_RSP IU Payload. The FCP_RES_IU Payload is used to transport FICON ending status along with the control unit queue time, disconnect time, active time, the offset of the last DCW executed, the residual data byte count of the last DCW executed, the residual data byte count of the CCWD, and possible sense data.
In a further example, to write 4k of customer data, the channel uses the FCP link protocol phases, as follows:

    
    
        1. Transfer the CCWD in the FCP_CMND IU.
        2. Transfer the IU of data, and sequence initiative to the control unit. (FCP Transfer Ready Disabled)
        3. Final status is sent in a FCP status frame that has a bit active in, for instance, byte 10 or 11 of the FCP_RSP IU Payload. The FCP_RES_INFO field or sense field is used to transport FICON ending status along with the control unit queue time, disconnect time, active time, the offset of the last DCW executed, the residual data byte count of the last DCW executed, the residual data byte count of the CCWD, and possible sense data.
    
    


By executing the TCW channel program of FIG. 4, there is only one exchange opened and closed (see also FIG. 5), instead of two exchanges for the CCW channel program of FIG. 2b (see also FIG. 3). Further, for the TCW channel program, there are three communication sequences (see FIGS. 4-5), as compared to seven sequences for the CCW channel program (see FIGS. 2b-3).
The number of exchanges and sequences remain the same for a TCW channel program, even if additional commands are added to the program. Compare, for example, the communications of the CCW channel program of FIG. 6 with the communications of the TCW channel program of FIG. 7. In the CCW channel program of FIG. 6, each of the commands (e.g., define extent command 600, locate record command 601, read command 602, read command 604, read command 606, locate record command 607 and read command 608) are sent in separate sequences from the channel 610 to the control unit 612. Further, each 4k block of data (e.g., data 614-620) is sent in separate sequences from control unit 612 to channel 610. This CCW channel program requires two exchanges to be opened and closed (e.g., open exchanges 622, 624 and close exchanges 626, 628), and fourteen communications sequences. This is compared to the three sequences and one exchange for the TCW channel program of FIG. 7, which accomplishes the same task as the CCW channel program of FIG. 6.
As depicted in FIG. 7, a channel 700 opens an exchange with a control unit 702 and sends a channel command word descriptor 704 to the control unit. The CCWD includes the define extent command, the two locate record commands, and the four read commands, as described above. In response to receiving the CCWD, the control unit executes the commands and sends, in a single sequence, the 16k of data 706 to the channel. Additionally, the control unit provides status to the channel and closes the exchange 708. Thus, the TCW channel program requires much less communications to transfer the same amount of data as the CCW channel program.
Further details regarding the transport control word, the channel command word descriptor and status are described with reference to FIGS. 8-10. In particular, one embodiment of a transport control word is described with reference to FIG. 8, one embodiment of a channel command word descriptor referred to by the transport control word is described with reference to FIG. 9, and one embodiment of ending status also referred to by the transport control word is described with reference to FIG. 10.
Referring to FIG. 8, in one example, a transport control word 800 includes a plurality of fields, such as, for instance:

    
    
        a) Command Field 802: The command field indicates if the command is a TCW channel command or a legacy channel CCW. A TCW channel command is an X8 command with X not equal to zero. As examples, the X8 command field includes one of the following commands:
        
            1) For x=one, as one example, the command is a write TCW command that transfers a channel command word descriptor to the control unit, as well as customer data, per the channel command word descriptor data byte count field in the transport control word; and
            2) For x=two, as one example, the command is a read TCW command that transfers a channel command word descriptor to the control unit, and the channel command word descriptor data byte count is the total amount of data the control unit will transfer to the channel;
        
        
        b) Flags 804: The flag field may include one or more flags. In this example, it includes a MIDAW flag that indicates whether modified indirect addressing or direct addressing is being used. If the flag is active, an address 810 in the transport control word is the address of a first modified indirect data address word (MIDAW) of a modified indirect data address list (MIDAL). Otherwise, the address is a data address used for direct addressing;
        c) CCWD Length 806: This field includes the length of the channel command word descriptor specified by this transport control word;
        d) CCWD Data Byte Count 808: This field includes the total amount of customer data to be transferred by all of the descriptor command words (DCWs), described below, in the channel command word descriptor;
        e) Address of MIDAW or Data Address 810: This field provides the address of a MIDAW, assuming flag field 804 indicates it should be a MIDAW address, or an address of customer data;
        f) Address of the CCWD 812: This field includes an address to locate in memory the channel command word descriptor. The channel command word descriptor is further described below.
        g) Address of Status 814: This field includes an address to locate in memory an ending completion status for this transport control word. Further information regarding the ending status is described below.
    
    


The three addresses defined by the transport control word including, MIDAW or data address 810, CCWD address 812, and status address 814, are used by, for instance, a host bus adapter to execute the equivalent of a FCP operation. This enables the FCP link phases, instead of FICON phases, to be used in communications, thereby significantly increasing performance and efficiency of the channel subsystem.
As indicated above, the transport control word specifies a channel command word descriptor to be used. The channel command word descriptor includes the multiple commands to be executed by the control unit. The commands are executed independent of the channel in that status relative to execution of the individual commands is not tracked by the channel. The control unit receives the multiple commands as a single unit and has the responsibility of executing the commands, in an appropriate manner. In one example, the CCWD is sent to the control unit as the FCP_CMND IU payload in the FCP link protocol. By relieving the channel of the responsibility of tracking individual commands, performance of the channel is significantly enhanced. Moreover, the control unit benefits by seeing the entire channel program at one time.
One embodiment of a channel command word descriptor (CCWD) is described with reference to FIG. 9. A channel command word descriptor 900 has three main parts, including, for instance, a header 902, multiple DCWs 904 and descriptor data 906, each of which is described below.
CCWD header 902 includes the following fields, as one example:

    
    
        a) Channel Image Id 910: This field identifies the channel involved in the communication;
        b) Control Unit Image Id 912: This field identifies the control unit communicating with the channel identified by channel image id 910;
        c) Device Address 914: This field identifies the device coupled to the control unit that is involved in the I/O communications;
        d) Read or Write field 916: This field indicates whether the I/O operations are read or write;
        e) CDB CMD 918: This field is used to identify this as a CCWD;
        f) I/O Priority 920: This field indicates the priority of this I/O;
        g) CCWD Length 922: This field indicates the length of the CCWD;
        h) #DCWs 924: This field indicates the number of descriptor command words for this CCWD; and
        i) CCWD Data Byte Count 926: This field describes the total customer data to be transferred by the CCWD.
    
    


Each descriptor command word 904 includes a plurality of fields, such as, for instance:

    
    
        a) Command Field 930: This field includes the CCW command (e.g., control commands like define extent and locate record; read; write; etc.);
        b) Flag Field 932: This field may include one or more flags. In this example, flag field 932 includes a command chain flag indicating whether command chaining is present; and a descriptor data present flag indicating whether descriptor data is present in the CCWD following this DCW. This flag is active for write control, when the write control command requires descriptor data;
        c) Byte Count Field 934: If this is a control command, the count is the number of bytes of control data in the CCWD; otherwise, it is the count of customer data to be transferred by this DCW. If the DCW command is a command intermediate or a no op command, the byte count field is zero.
    
    


Descriptor data 906 includes the data 936 for a DCW write control command. This data is in the CCWD following the DCW the data is for and its presence is made known by the flag field in the DCW. By specifying control data directly in the descriptor list, the device can obtain the data without requiring the device to perform a separate data transfer to obtain it.
In one embodiment, a checking code, such as a cyclic redundancy check (e.g., FICON CRC), a longitudinal redundancy check (LRC), a checksum, etc., is applied across the CCWD data transferred per the sum of the DCW byte counts in the CCWD, and a separate checking code is applied to the CCWD, when it is transmitted to the control unit. For example, a checking code is applied to the total data being transferred by the CCWD. This is at a higher level than the CRC applied at the transport level. The check is applied to each data packet sent, and then accumulated and verified at the receiver end to ensure the entire data, as specified by the CCWD data byte count, arrived completely and without errors.
As a further example, for the CCWD itself, a checking code is applied. For instance, the code is appended to the information. The control unit receives the information, checks the code, and if valid, the information is considered valid.
The transport control word also specifies a location for ending status. This allows the operating system to specify an area in storage for the extra timers and count information from the control unit for a TCW operation and for sense data, thus, guaranteeing the delivery of concurrent sense data on every unit check condition. One example of ending status is described with reference to FIG. 10.
In one embodiment, an ending status control block 1000 includes the following fields:

    
    
        a) DCW Residual Byte Count 1002: This field indicates the residual byte count of a failed DCW (i.e., where execution of the DCWs was interrupted);
        b) Sense Length 1004: This field specifies the length of sense data appended at the end of this control block in appended sense data;
        c) Response Length 1006: This field indicates the length of the response portion of this control block;
        d) CH Image Id 1008: This field identifies the channel involved in the communication;
        e) CU Image Id 1010: This field identifies the control unit communicating with the channel identified by channel image id 1008;
        f) Device Address 1012: This field identifies the device coupled to the control unit that is involved in the I/O communications;
        g) Status Flags 1014: This field specifies one or more status flags. Examples of status flags are described in “Fibre Channel Single Byte Command Code Sets-2 Mapping Protocol (FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003), which is hereby incorporated herein by reference in its entirety;
        h) Status 1016: This field identifies status of the communication, including, for instance, device status, which is further described in “IBM® z/Architecture Principles of Operation,” Publication No. SA22-7832-04, 5th Edition, September 2005, hereby incorporated herein by reference in its entirety;
        i) CCWD Residual Byte Count 1020: This field indicates the residual byte count of the CCWD Data Byte Count, which is the remaining count of data that was not transferred for the whole CCWD;
        j) DCW Offset 1022: If all DCWs are not executed in the CCWD, this is the DCW offset in the CCWD of the failed DCW;
        k) Queue Time Parameter 1024: This field specifies the amount of time the control unit had the I/O operation on it's queue with the exchange open to the channel;
        l) Defer Time Parameter 1026: This field specifies the amount of time the control unit waited for the data, with the exchange open to the channel, because of a control unit data cache miss. The control unit had to access the media to reference the requested data;
        m) Control Unit Active Time 1028: This field specifies the time the control unit is active executing a TCW;
        n) Appended Sense Data, if any 1030: This field includes sense for the case the control unit encountered a unit check during the I/O operation.
    
    


Status is further described in “IBM® z/Architecture Principles of Operation,” Publication No. SA22-7832-04, 5th Edition, September 2005; and queue time, defer time and appended sense are further described in “Fibre Channel Single Byte Command Code Sets-2 Mapping Protocol (FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003), each of which is hereby incorporated herein by reference in its entirety.
For legacy FICON, the command response is an important measurement point in the operation of a CCW channel program. FIG. 11 is a timeline as seen by the channel that depicts various timing points kept track of by the channel subsystem for a CCW channel program. As an example, the channel sees Start subchannel A 1100, CMR B 1102, Disconnect C 1104, Reconnect D 1106 and Ending Status E 1108. The control unit provides the channel with the CU queue time and CU defer time at ending status time.
The legacy channel subsystem, in effect, performs a number of steps to gather various times for channel subsystem measurements. For example, with reference to FIG. 11, it timestamps the time of start Subchannel at A 1100, and it timestamps the time of CMR at B 1102. At disconnect time C 1104, it calculates connect time (CT=C−B). It timestamps the time of reconnect at D 1106, and timestamps Ending Status time at E 1108. From there, it calculates total connect time CT=(C−B)+(E−D); total start pending time SP=(B−A); and disconnect time DT=(E−A)−CT−SP).
For a TCW, however, the channel does not get a Command Response CMR to know when the control unit started the I/O operation. For instance, with reference to the timeline of FIG. 12, it only sees the Start Subchannel A 1200 and the Ending status E 1202. The channel does not see for a TCW operation the CMR B 1204 time, and the time required to retrieve data from the media starting at C 1206 and ending at D 1208. The time to retrieve data from the media is part of the CU defer time for a TCW. The CU queue time (not shown) and CU defer time are provided by the control unit at ending status time.
Thus, for a TCW channel program, the channel timestamps the time of Start Subchannel at A 1200 and the ending status time at E 1202, but it is the control unit that performs the tracking of when the operation started and the total time to execute the individual commands and provide this measurement data as part of the ending status.
As one example, the control unit reports the following at ending status:

    
    
        AT=Active time=(C−B)+(E−D) in FIG. 12—this is CU active time 1028 in FIG. 10;
        QT=CU queue time—this is the amount of time the control unit had the operation on it's queue before starting the operation and is the queue time parameter 1024 in FIG. 10; and
        DT=Defer time=(D−C) in FIG. 12—this is defer time parameter 1026 in FIG. 10.
    
    


From the timers provided by the control unit and the beginning and ending timestamps provided by the channel subsystem at A and E on FIG. 12, the same measurement data is provided for a TCW command as for the legacy CCW commands. The I/O subsystem determines:

    
    
        CMR time (B−A (FIG. 12))=(E−A)−AT−DT−QT;
        Total connect time CT=CU reported active time AT (1028 in FIG. 10);
        Total start pending time SP=(E−A)−AT−DT; and
        Disconnect time=CU reported defer time=(D−C) (1026 in FIG. 10).
    
    


Therefore, the control unit has the responsibility of tracking state information of the individual commands and providing measurement data relating thereto, relieving the channel of this responsibility. The operating system communicates directly with the control unit using the channel only as a conduit. The channel does not track the state information of the individual commands but the I/O subsystem provides the same measurement data as with legacy CCWs by using the I/O subsystem timestamps A and E and the three timers from the control unit, and thus, the same measurement data is provided to the operating system. At the same time, the workload of the channel is reduced.
One or more aspects of the present invention can be included in an article of manufacture (e.g., one or more computer program products) having, for instance, computer useable media. The media has therein, for instance, computer readable program code means or logic (e.g., instructions, code, commands, etc.) to provide and facilitate the capabilities of the present invention. The article of manufacture can be included as a part of a computer system or sold separately.
One example of an article of manufacture or a computer program product incorporating one or more aspects of the present invention is described with reference to FIG. 13. A computer program product 1300 includes, for instance, one or more computer usable media 1302 to store computer readable program code means or logic 1304 thereon to provide and facilitate one or more aspects of the present invention. The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. Examples of a computer readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.
A sequence of program instructions or a logical assembly of one or more interrelated modules defined by one or more computer readable program code means or logic direct the performance of one or more aspects of the present invention.
Advantageously, in accordance with one or more aspects of the present invention, I/O processing is enhanced by enabling the operating system to communicate directly with the control units and by relieving the I/O communications adapters of having to track all the state information regarding individual commands being processed. That is, a direct communication path is established between an operating system and a control unit, such that the operating system can deliver a list of command words to the device through the channel subsystem without the channel subsystem requiring any visibility to or processing of the individual commands. This reduces the work of the communications adapter, and enhances the performance thereof. Further, the control unit is benefited by having an understanding of all the commands to be performed by the control unit for a channel program. Additionally, more precise measurement data is provided by having the control unit provide the various times for intervals it controls directly, rather than having the channel subsystem infer the times from imprecise signals on the interface.
In accordance with one or more aspects of the present invention, well behaved (e.g., predictable execution known by the operating system or software at build time) CCW chains are collapsed into one control block referred to herein as the CCW Descriptor (CCWD) and is referenced by a CCW referred to herein as the transport control word. Command chain CCWs, as well as data chain CCWs, may be collapsed into one CCWD. This reduces the number of sequences and exchanges required to transfer a given amount of data. Instead of requiring separate sequences for individual device commands, a single exchange is used. As one example, this results in a 2× reduction over FICON in both exchanges and sequences required to transfer 4 k of data. This enables FICON to be competitive with FCP particularly on small block transfers. Instead of using the FICON link phases, FCP link phases are used. However, the information that is in the FCP_CMND IU and FCP_RSP IU is not FCP, except for bits and bytes that have to be sent in the FCP_CMND IU to allow a FCP host bus adapter to work with the protocol.
The TCW provides the information for an I/O communications adapter to transport the list of CCW commands to the control unit, as well as transfers customer data to or from the control unit. Advantageously, a channel subsystem using one or more aspects of the present invention can also continue to use CCW channel programs, as well as the TCW channel programs. By using TCWs, the performance of an I/O operation that transfers, for instance, small blocks of data is improved. Moreover, the use of TCWs and CCWDs enables a place for sense data, which may be sent with the ending status.
Although various embodiments are described above, these are only examples. Processing environments other than those described herein, including others that use I/O subsystems, other than channel subsystems, can incorporate and use one or more aspects of the present invention. Further, although various control blocks have been shown, the location of the information within those control blocks may be other than shown herein. Further, each control block may include additional, less or different information than described herein. For instance, there may be additional, fewer and/or different fields, including fields that may include additional, fewer and/or different flags. Further, there may be additional, fewer and/or different field sizes. Yet further, although main memory is mentioned or described in various portions of the embodiment, one or more aspects of the present invention may be applicable to other memory. Still further, although communications protocols, such as FICON and FCP, are described herein, one or more aspects of the present invention are applicable to other protocols.
Moreover, an environment may include an emulator (e.g., software or other emulation mechanisms), in which a particular architecture or subset thereof is emulated. In such an environment, one or more emulation functions of the emulator can implement one or more aspects of the present invention, even though a computer executing the emulator may have a different architecture than the capabilities being emulated. As one example, in emulation mode, the specific instruction or operation being emulated is decoded, and an appropriate emulation function is built to implement the individual instruction or operation.
In yet other examples, TCW channel programs performing other commands may include one or more aspects of the present invention. Further, TCW channel programs can read other amounts of data than described herein and still benefit from one or more aspects of the present invention. Numerous other examples and modifications are possible without departing from the spirit of the present invention.
In an emulation environment, a host computer includes, for instance, a memory to store instructions and data; an instruction fetch unit to fetch instructions from memory and to optionally, provide local buffering for the fetched instruction; an instruction decode unit to receive the instruction fetch unit and to determine the type of instructions that have been fetched; and an instruction execution unit to execute the instructions. Execution may include loading data into a register for memory; storing data back to memory from a register; or performing some type of arithmetic or logical operation, as determined by the decode unit. In one example, each unit is implemented in software. For instance, the operations being performed by the units are implemented as one or more subroutines within emulator software.
Further, a data processing system suitable for storing and/or executing program code is usable that includes at least one processor coupled directly or indirectly to memory elements through a system bus. The memory elements include, for instance, local memory employed during actual execution of the program code, bulk storage, and cache memory which provide temporary storage of at least some program code in order to reduce the number of times code must be retrieved from bulk storage during execution.
Input/Output or I/O devices (including, but not limited to, keyboards, displays, pointing devices, etc.) can be coupled to the system either directly or through intervening I/O controllers. Network adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modems, and Ethernet cards are just a few of the available types of network adapters.
The capabilities of one or more aspects of the present invention can be implemented in software, firmware, hardware, or some combination thereof. At least one program storage device readable by a machine embodying at least one program of instructions executable by the machine to perform the capabilities of the present invention can be provided.
The flow diagrams depicted herein are just examples. There may be many variations to these diagrams or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. All of these variations are considered a part of the claimed invention.
Although preferred embodiments have been depicted and described in detail there, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.

## Claims

1. A method of facilitating input/output processing of a processing environment, said method comprising:
obtaining by an input/output communications adapter of the processing environment a transport control word, said transport control word including a count of the total amount of data being transferred, an address of a descriptor control block to be sent to a control unit of the processing environment, in which the descriptor control block includes a plurality of input/output commands to be executed, an address of a list that informs the input/output communications adapter where to store or fetch data received from or transmitted to the control unit, and an address where to store ending status from the control unit;
forwarding from the input/output communications adapter to the control unit the descriptor control block that includes the plurality of input/output commands as one entity, wherein the forwarding includes forwarding from the input/output communications adapter to the control unit the descriptor control block including the plurality of input/output commands in a single communication; and
executing by the control unit the plurality of input/output commands to perform one or more input/output operations, wherein the executing is performed absent a tracking by the input/output communications adapter of state relative to the individual input/output commands of the plurality of input/output commands being executed by the control unit.

2. The method of claim 1, wherein the descriptor control block further comprises a header providing information relating to the input/output commands to be executed and descriptor data for one or more of the input/output commands.

3. The method of claim 2, wherein the descriptor data comprises control data to be provided to a device coupled to the control unit, the device designated by a device address specified in the header of the descriptor control block, said control data being provided to the device absent a separate data transfer.

4. The method of claim 1, further comprising applying a checking code to the descriptor control block to enable the control unit to check validity of the descriptor control block.

5. The method of claim 1, wherein the list comprises one or more modified indirect data address words.

6. The method of claim 5, wherein the list of one or more modified indirect data address words comprises a single modified indirect data address word list that describes a plurality of data areas for a plurality of descriptor command words.

7. The method of claim 1, wherein a transfer of data resulting from the execution of the plurality of input/output commands is performed using a single exchange between the input/output communications adapter and the control unit.

8. The method of claim 7, further comprising applying a checking code to the data being transferred to check validity of the transferred data.

9. The method of claim 1, further comprising providing by the control unit to the input/output communications adapter at least one of data and status resulting from execution of the plurality of input/output commands, wherein a transfer of data resulting from the execution of the plurality of input/output commands is performed using three communication sequences between the input/output communications adapter and control unit.

10. The method of claim 9, wherein the number of sequences remains the same, even if the number of input/output commands indicated by the location specified in the transport control word increases.

11. The method of claim 1, wherein the input/output communications adapter comprises a channel, and the plurality of input/output commands comprise a plurality of channel commands specified by one or more channel command words, wherein each channel command word comprises a command code, one or more flags and a count field.