Title of Invention

PROVIDING INDIRECT DATA ADDRESSING IN INPUT/OUTPUT PROCESSING SYSTEM WHERE INDIRECT DATA ADDRESS LIST IS NON-CONTIGUOUS"

Abstract Systems, methods and computer program products for providing indirect data addressing at an I/O subsystem of an I/O processing system. 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 a method. The method includes receiving a control word for an I/O operation. The control word includes an indirect data address for data associated with the I/O operation. The indirect data address includes a starting location of a list of storage addresses that collectively specify the data, the list spans two or more non-contiguous storage locations. Data is gathered responsive to the list. The gathered data is transmitted to a control unit in the I/O processing system. FIG. 10
Full Text FIELD OF THE INVENTION
The disclosure relates generally to input/output processing, and in particular, to providing a
non-contiguous indirect data addressing list at an I/O subsystem of an I/O processing system.
DESCRIPTION OF BACKGROUND
Input/output (I/O) operations are used to transfer data between memory and I/O devices of
an I/O processing system. Specifically, data is written from memory to one or more I/O
devices, and data is read from one or more I/O devices to memory by executing I/O
operations.
To facilitate processing of I/O operations, an I/O subsystem of the I/O processing system is
employed. The I/O subsystem is coupled to main memory and the I/O devices of the I/O
processing system and directs the flow of information between memory and the I/O devices.
One example of an I/O 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 I/O devices.
The channel subsystem may employ channel command words (CCWs) to transfer data
between the I/O devices and memory. A CCW specifies the command to be executed. For
commands initiating certain I/O operations, the CCW designates the memory area associated
with the operation, the action to be taken whenever a transfer to or from the area is
completed, and other options.
During I/O processing, a list of CCWs is fetched from memory by a channel. The channel
parses each command from the list of CCWs and forwards a number of the commands, each
command in its 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 its own entity. Further, the channel
infers certain information associated with processing the response from the control unit for
each command.
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Performing I/O processing on a per CCW basis may involve a large amount of processing
overhead for the channel subsystem, as the channels parse CCWs, track state information,
and react to responses from the control units. Therefore, it may be beneficial to shift much
of the processing burden associated with interpreting and managing CCW and state
information from the channel subsystem to the control units. Simplifying the role of
channels in communicating between the control units and an operating system in the I/O
processing system may increase communication throughput as less handshaking is
performed. However, altering command sequences, as well as roles of the channel
subsystem and the control units, allows the amount of data that is transferred within a single
I/O operation to more than one megabyte. This is the maximum amount of data that can be
transferred with one continuous list of transport indirect data addresses when the system
page size is 4k bytes. Currently, an existing Channel Command Word (CCW) cannot
support a data transfer of more than 64k bytes within a single I/O operation because of the
limitation of the two byte count field in the CCW. The Transport Control Word (TCW)
solved that problem by increasing the byte count to four bytes in the TCW, but then the next
limitation of one megabyte was encountered because the transport indirect data address list
(TIDAL) must be contained in one page which is 4k bytes which only allowed 256 address
list entries.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter which is regarded as the invention is particularly pointed out and
distinctly claimed 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 an I/O processing system incorporating and using one or
more aspects of the invention;
FIG. 2A depicts one example of a prior art channel command word;
FIG. 2B depicts one example of a prior art channel command word channel program;
FIG. 3 depicts one embodiment of a prior art link protocol used in communicating between a
channel and control unit to execute the channel command word channel program of FIG. 2B;
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FIG. 4 depicts one embodiment of a transport control word channel program, in accordance
with an aspect of the 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 invention;
FIG. 6 depicts one embodiment of a prior art link protocol used to communicate between a
channel and control unit in order to execute four write 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 write commands of a transport control word channel
program, in accordance with an aspect of the invention;
FIG. 8 depicts one embodiment of a control unit and a channel subsystem, in accordance
with an aspect of the invention;
FIG. 9 depicts one embodiment of a transport mode indirect data address word (TIDAW), in
accordance with an aspect of the invention;
FIG. 10 depicts one embodiment of a process for providing non-contiguous indirect data
addressing at an I/O subsystem; and
FIG. 11 depicts one embodiment of an article of manufacture incorporating one or more
aspects of the invention.
The detailed description explains the preferred embodiments of the invention, together with
advantages and features, by way of example with reference to the drawings.
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the invention include a computer program product for providing indirect
data addressing at an input/output (I/O) subsystem of an I/O processing system. 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 a
method. The method includes receiving a control word for an I/O operation. The control
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word includes an indirect data address for data associated with the I/O operation. The
indirect data address includes a starting location of a list of storage addresses that
collectively specify the data, the list spans two or more non-contiguous storage locations.
Data is gathered responsive to the list. The gathered data is transmitted to a control unit in
the I/O processing system.
Additional embodiments include an apparatus for providing indirect data addressing at an
I/O subsystem of an I/O processing system. The apparatus includes an I/O subsystem
adapted to communicate with a control unit in the I/O processing system. The I/O
subsystem performs a method including receiving a control word for an I/O operation. The
control word includes an indirect data address for data associated with the I/O operation.
The indirect data address includes a starting location of a list of storage addresses that
collectively specify the data, the list spans two or more non-contiguous storage locations.
Data is gathered responsive to the list. The gathered data is transmitted to the control unit.
Further embodiments include a method for providing indirect data addressing at an I/O
subsystem of an I/O processing system. The method includes receiving a control word for
an I/O operation. The control word includes an indirect data address for data associated with
the I/O operation. The indirect data address includes a starting location of a list of storage
addresses that collectively specify the data, the list spans two or more non-contiguous
storage locations. Data is gathered responsive to the list. The gathered data is transmitted to
a control unit in the I/O processing system.
Still further embodiments include a computer program product for providing indirect data
addressing at an I/O subsystem of an I/O processing system. 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 a method. The method includes
receiving a control word for an I/O operation. The control word includes an indirect data
address for customer data output from the I/O operation. The indirect data address includes
a starting location of a list of storage addresses that collectively specify a storage location for
the customer data output, the list spans two or more non-contiguous storage locations.
Customer data output is received from a control unit in the I/O processing system in
response to the I/O operation being executed at the control unit. The customer data output is
stored at the storage location at the I/O subsystem responsive to the list.
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Other articles of manufacture, apparatuses, and/or methods according to embodiments will
be or become apparent to one with skill in the art upon review of the following drawings and
detailed description. It is intended that all such additional articles of manufacture,
apparatuses, and/or methods be included within this description, be within the scope of the
invention, and be protected by the accompanying claims.
In accordance with an aspect of the invention, input/output (I/O) processing is facilitated.
I/O processing is facilitated, in one example, by reducing communications between
components of an I/O processing system used to perform the I/O processing. For instance,
the number of exchanges and sequences between an 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 block, referred to herein as a transport
command control block (TCCB), an address of which is specified in a transport control word
(TCW). The TCW is sent from an operating system (OS) or other application to the I/O
communications adapter, which in turn forwards the TCCB in a command message 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.
The plurality of commands is also referred to as a channel program, which is parsed and
executed on the control unit rather than the I/O communications adapter.
In an exemplary embodiment, the TCW for an I/O operation includes pointers indicating the
location of the control data (e.g., the TCCB) and the customer data associated with the I/O
operation. In an exemplary embodiment, the pointers refer to an indirect data address,
referred to herein as a transport mode indirect data address list (TIDAL). The TIDAL
includes a list of addresses where the data is located; these addresses are referred to herein as
transport mode indirect data address words (TIDAWs). In the current system design with
4K pages the TIDAL cannot be larger than four kilobytes (4K), thus limiting the number of
continuous TIDAWs that may be included in a single TIDAL to 256 (each TIDAL is 16
bytes). This limits the total amount of data that can be transferred by one I/O operation to
one megabyte assuming 4K pages, each TIDAL is 16 bytes and the TIDAL has to be
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contained in one 4K page. In an exemplary embodiment of the invention, this limitation is
removed by allowing a TIDAW address to indicate the starting location of the next
TIDAWs at another storage location which may be in a different page. A flag in the
TIDAW is utilized to indicate whether the address of the TIDAW includes a data address or
an address of the continuation of the TIDAW list. In this manner, TIDAWs making up a
single TIDAL can be located in non-contiguous storage locations and thus, more than 256
TIDAWs can be included in a single TIDAL list. This allows more data to be transferred
within a single I/O operation. For example, in an exemplary embodiment, where the count
field in the TCW is four bytes, about four gigabytes (four gigabytes minus one byte) may be
transferred within a single I/O operation.
One example of an I/O processing system incorporating and using one or more aspects of the
invention is described with reference to FIG. 1. I/O processing system 100 includes a host
system 101, which further includes for instance, a main memory 102, one or more central
processing units (CPUs) 104, a storage control element 106, and a channel subsystem 108.
The host system 101 may be a large scale computing system, such as a mainframe or server.
The I/O processing system 100 also includes one or more control units 110 and one or more
I/O devices 112, each of which is described below.
Main memory 102 stores data and programs, which can be input from I/O devices 112. For
example, the main memory 102 may include one or more operating systems (OSs) 103 that
are executed by one or more of the CPUs 104. For example, one CPU 104 can execute a
Linux® operating system 103 and a z/OS® operating system 103 as different virtual
machine instances. The main memory 102 is directly addressable and provides for highspeed
processing of data by the CPUs 104 and the channel subsystem 108.
CPU 104 is the controlling center of the I/O processing system 100. It contains sequencing
and processing facilities for instruction execution, interruption action, timing functions,
initial program loading, and other machine-related functions. CPU 104 is coupled to the
storage control element 106 via a connection 114, such as a bidirectional or unidirectional
bus.
Storage control element 106 is coupled to the main memory 102 via a connection 116, such
as a bus; to CPUs 104 via connection 114; and to channel subsystem 108 via a connection
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118. Storage control element 106 controls, for example, queuing and execution of requests
made by CPU 104 and channel subsystem 108.
In an exemplary embodiment, channel subsystem 108 provides a communication interface
between host system 101 and control units 110. Channel subsystem 108 is coupled to
storage control element 106, as described above, and to each of the control units 110 via a
connection 120, such as a serial link. Connection 120 may be implemented as an optical
link, employing single-mode or multi-mode waveguides in a Fibre Channel fabric. Channel
subsystem 108 directs the flow of information between I/O devices 112 and main memory
102. It relieves the CPUs 104 of the task of communicating directly with the I/O devices
112 and permits data processing to proceed concurrently with I/O processing. The channel
subsystem 108 uses one or more channel paths 122 as the communication links in managing
the flow of information to or from I/O devices 112. As a part of the I/O processing, channel
subsystem 108 also performs the path-management functions of testing for channel path
availability, selecting an available channel path 122 and initiating execution of the operation
with the I/O devices 112.
Each channel path 122 includes a channel 124 (channels 124 are located within the channel
subsystem 108, in one example, as shown in FIG. 1), one or more control units 110 and one
or more connections 120. In another example, it is also possible to have one or more
dynamic switches (not depicted) as part of the channel path 122. A dynamic switch is
coupled to a channel 124 and a control unit 110 and provides the capability of physically
interconnecting any two links that are attached to the switch. In another example, it is also
possible to have multiple systems, and therefore multiple channel subsystems (not depicted)
attached to control unit 110.
Also located within channel subsystem 108 are subchannels (not shown). One subchannel is
provided for and dedicated to each I/O device 112 accessible to a program through the
channel subsystem 108. 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 I/O device 112 and its attachment to channel subsystem 108. The
subchannel also provides information concerning I/O operations and other functions
involving the associated I/O device 112. The subchannel is the means by which channel
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subsystem 108 provides information about associated I/O devices 112 to CPUs 104, which
obtain this information by executing I/O instructions.
Channel subsystem 108 is coupled to one or more control units 110. Each control unit 110
provides logic to operate and control one or more I/O devices 112 and adapts, through the
use of common facilities, the characteristics of each I/O device 112 to the link interface
provided by the channel 124. The common facilities provide for the execution of I/O
operations, indications concerning the status of the I/O device 112 and control unit 110,
control of the timing of data transfers over the channel path 122 and certain levels of I/O
device 112 control.
Each control unit 110 is attached via a connection 126 (e.g., a bus) to one or more I/O
devices 112. I/O devices 112 receive information or store information in main memory 102
and/or other memory. Examples of I/O devices 112 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 I/O processing system 100 are further described
in “IBM® z/Architecture Principles of Operation,” Publication No. SA22-7832-05, 6th
Edition, April 2007; U.S. Patent 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 October 24, 1995;
and U.S. Patent No. 5,526,484 entitled “Method And System For Pipelining The Processing
Of Channel Command Words,” Casper et al., issued June 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, New York, 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 I/O devices 112 and memory 102, channel
command words (CCWs) are used. A CCW specifies the command to be executed, and
includes other fields to control processing. One example of a CCW is described with
reference to FIG. 2A. A CCW 200 includes, for instance, a command code 202 specifying
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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 Serial Number 11/464,613, entitled “Flexibly Controlling The Transfer Of Data
Between Input/Output Devices And Memory,” Brice et al., filed August 15, 2006, which is
hereby incorporated herein by reference in its entirety.
One or more CCWs arranged for sequential execution form a channel program, also referred
to herein as a CCW channel program. The CCW channel program is set up by, for instance,
an 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 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
write CCWs 221. Each write 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-3 Mapping Protocol (FC-SB-3), T11/Project
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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 300 uses TIC 218 to locate the locate record CCW and the write
CCW. It fetches the locate record command and data 306 (FIG. 3) from the locate record
CCW 217 (FIG. 2B) and locate record data 220. The write command and data 308 (FIG. 3)
is fetched from write CCW 221 and data area 224 (FIG. 2B). Each is sent to the control unit
302.
The control unit 302 opens an exchange 310 with the channel 300, in response to the open
exchange of the channel 300. This can occur before or after locate command and data 306
and/or write command and data 308. Along with the open exchange, a response (CMR) is
forwarded to the channel 300. The CMR provides an indication to the channel 300 that the
control unit 302 is active and operating.
The control unit 302 provides the status to the channel 300 and closes the exchange 312. In
response thereto, the channel 300 stores the data, examines the status and closes the
exchange 314, which indicates to the control unit 302 that the status has been received.
The processing of the above CCW channel program to write 4k of data requires two
exchanges to be opened and closed and six sequences. The total number of exchanges and
sequences between the channel and control unit is reduced through collapsing multiple
commands of the channel program into a TCCB. The channel, e.g., channel 124 of FIG. 1,
uses a TCW to identify the location of the TCCB, as well as locations for accessing and
storing status and data associated with executing the channel program. The TCW is
interpreted by the channel and is not sent or seen by the control unit.
One example of a channel program to write 4k of data, as in FIG. 2B, but includes a TCCB,
instead of separate individual CCWs, is described with reference to FIG. 4. As shown, a
channel program 400, referred to herein as a TCW channel program, includes a TCW 402
specifying a location in memory of a TCCB 404, as well as a location in memory of a data
area 406 or a TIDAL 410 (i.e., a list of transport mode indirect data address words
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(TIDAWs), similar to MIDAWs) that points to data area 406, and a status area 408. TIDAW
zero 412, TIDAW one 414 and TIDAW two 416 (collectively TIDAWs 412 – 416) can
reference different locations in the data area 406 for acquiring or storing data. The TIDAWs
412 – 416 can reference non-contiguous blocks of data or contiguous blocks of data. The
TIDAWs 412 – 416 in TIDAL 410 may be located sequentially in memory or located noncontiguously
relative to each other. While only three TIDAWs 412 – 416 are depicted in
TIDAL 410, it will be understood that any number of TIDAWs can be included in the
TIDAL 410.
The processing of a TCW channel program is described with reference to FIG. 5. The link
protocol used for these communications is, for instance, Fibre Channel Protocol (FCP). In
particular, three phases of the FCP link protocol are used, allowing host bus adapters to be
used that support FCP to perform 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, September 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
TCCB 504 to the control unit 502. In one example, the TCCB 504 and sequence initiative
are transferred to the control unit 502 in a FCP command, referred to as FCP_CMND
information unit (IU) or a transport command IU. The control unit 502 transmits a transfer
ready (XFER_RDY) IU 510 to the channel 500 when it is ready to receive data for the write
commands received in the TCCB 504. In response to receiving the XFER_RDY IU 510, the
channel 500 transfers the data 506 to the control unit 502, via, for instance, a FCP_Data IU.
The control unit 502 executes the multiple commands of the TCCB 504 (e.g., define extent
command, locate record command, write command as device control words (DCWs)) and
writes the data 506 received from the channel 500. 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 payload of a FCP_RSP IU, also referred to as a transport
response IU. The FCP_RSP IU payload may be used to transport FICON ending status
along with additional status information.
The embodiment of the link protocol depicted in FIG. 5 is utilized when XFER_RDY is
enabled. In the embodiment depicted in FIG. 5, the channel 500 cannot send the data 506 to
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the control unit 502 until it is requested by the control unit 502 via the XFER_RDY IU 510.
In an alternate exemplary embodiment, XFER_RDY is disabled and the control unit does not
transmit a XFER_RDY IU 510 to the channel 500. Thus, the channel 500 does not have to
wait for the control unit 502 to request the data 506 before sending the data 506. This
alternate embodiment, where XFER_RDY is disabled may be utilized when the channel 500
and the control unit 502 are located geographically far apart from each other (e.g., greater
than twenty kilometers, greater than fifty kilometers) to improve performance. Unless
otherwise specified, the discussion herein assumes that XFER_RDY is enabled.
In a further example, to write 4K of customer data, the channel 500 uses the FCP link
protocol phases, as follows:
1. Transfer a TCCB in the FCP_CMND IU and sequence initiative to the control
unit 502.
2. Wait for a XFER_RDY IU indicating that the control unit is ready to receive the
data.
3. Transfer the IU of data, and sequence initiative to the control unit 502.
4. 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_RSP_INFO field or sense field is used to
transport FICON ending status along with additional status information.
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 four communication
sequences (see FIGs. 4-5), as compared to six 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 and data 600, locate record command and data 601,
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write command and data 602, write command and data 604, locate record command and data
606, write command and data 608, and write command and data 620) are sent in separate
sequences from channel 610 to control unit 612. This CCW channel program requires two
exchanges to be opened and closed (e.g., open exchanges 622, 624 and close exchanges 626,
628), and ten communications sequences. This is compared to the four 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
TCCB 704 to the control unit 702. The TCCB 704 includes the define extent command, the
two locate record commands, and the four write commands in DCWs, as described above.
Similar to the example depicted in FIG. 5, the control unit 702 may use an XFER_RDY IU
710 to notify the channel 700 that it is ready receive data, provided that XFER_RDY support
is not disabled. The channel 700 transmits 16k of data 706 to the control unit 702 in a single
sequence upon receipt of the XFER_RDY IU 710. The channel 700 inserts a CRC every 4K
of the 16k of data 706 in the sequence. The insertion of a CRC every 4K allows the control
unit 702 to verify the 16K of data incrementally, rather than buffer the entire 16K for
verification before completing the write commands in the TCCB 704. Additionally, the
control unit 702 provides status to the channel 700 and closes the exchange 708. Thus, the
TCW channel program of FIG. 7 requires much less communications to transfer the same
amount of data as the CCW channel program of FIG. 6, while supporting incremental data
verification via multiple CRC insertion in the output data stream from the channel 700.
Turning now to FIG. 8, one embodiment of channel 124 in the channel subsystem 108 and
the control unit 110 of FIG. 1 that support TCW channel program execution are depicted in
greater detail. The control unit 110 includes CU control logic 802 to parse and process
messages containing a TCCB, such as the TCCB 704 of FIG. 7, as well as data received
from the channel 124 via the connection 120. The CU control logic 802 can extract DCWs
and control data from the TCCB received at the control unit 110 to control a device, for
instance, I/O device 112 via connection 126. The CU control logic 802 sends device
commands and data to the I/O device 112, and receives status information and other
feedback from the I/O device 112. When the CU control logic 802 receives data, such as the
first checking block boundary of the 16K bytes of data 706 of FIG. 7, the CU control logic
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802 writes this data received into data buffer 804 for temporary storage, until the CRC is
received for the checking block boundary is checked, then that data may be sent to the I/O
device 112. This continues for each checking block boundary until the I/O operation is
completed.
The control unit 110 may further include other queue or memory elements (not depicted) for
storing additional message or status information associated with communications between
the channel 124 and the I/O device 112.
The channel 124 in the channel subsystem 108 includes elements to support communication
with the control unit 110. For example, the channel 124 may include CHN control logic 806
that interfaces with the gather data logic 812. The gather data logic 812 is described herein
below in reference to FIG. 10. In an exemplary embodiment, the CHN control logic 806
controls communication between the channel subsystem 108 and the control unit 110. The
CHN control logic 806 may directly interface to the CU control logic 802 via the connection
120 to send commands and receive responses, such as transport commands and response
IUs. Alternatively, messaging interfaces and/or additional buffers (not depicted) can be
placed between the CHN control logic 806 and the CU control logic 802. The CHN
subsystem registers 814 can include fixed values that provide configuration and status
information, as well as dynamic status information, updated as commands are transported
and responses are received. The CHN subsystem registers 814 may be dedicated hardware
registers and/or virtual registers established using memory mapping.
In one embodiment, the CHN subsystem registers 814 include the TIDAL 410 and TIDAWs
412 – 416 of FIG. 4 as memory mapped registers.
One example of a TIDAW 900 is depicted in FIG. 9. The TIDAW 900 provides indirect
addressing to data used in a TCW channel program, such as the TIDAWs 412 – 416 of FIG.
4. The TIDAW 900 includes flags 902, a count 904, and an address 906. Each field (i.e.,
flags 902, count 904, and address 906) in the TIDAW format 900 is assigned to a particular
byte address to support parsing of the fields. Although one arrangement of fields within the
TIDAW 900 is depicted in FIG. 9, it will be understood that the order of fields can be
rearranged to alternate orderings.
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In an exemplary embodiment, the flags 902 include a last TIDAW flag and a transporttransfer
in channel (T-TIC) flag, in addition to other flags. The last TIDAW flag indicates
that the associated TIDAW is the last TIDAW in a TIDAL, consistent with the definition for
a MIDAW. When count 904 goes to zero with the last TIDAW flag set, the data transfer for
the associated I/O operation is complete. The T-TIC flag indicates whether the contents of
the address 906 include data or the address of the next TIDAW in the TIDAL. In an
exemplary embodiment, when the T-TIC flag is set, then the address 906 in the TIDAW is
the address of the next TIDAW in the TIDAL. In the manner, the address 906 may be
utilized to access a TIDAW at a non-contiguous storage location from the current TIDAW.
Thus, the TIDAW list can contain more than 256 entries, thereby exceeding the maximum
number of allowable indirect data address words in current implementations. In an
exemplary embodiment, when the T-TIC flag is set the address 906 must have the four low
order bits set to zero because the 16 byte TIDAW must be on a 16 byte address boundary.
When the T-TIC flag is not set, then the address 906 in the TIDAW is the address of a
portion of the data that makes up the data being gathered for the I/O operation. The size of
the data is indicated in the count field 904. If the last TIDAW flag and the T-TIC flag are
not set, then the next TIDAW is located in the next storage location (e.g., it is contiguous to
the current TIDAW).
Turning now to FIG. 10, a process 1000 for gathering data for an I/O operation will now be
described in accordance with exemplary embodiments, and in reference to the I/O processing
system 100 of FIG. 1. At block 1002, the channel subsystem 108 receives a control word for
an I/O operation (e.g., a TCW). The control word includes an indirect data address that
points to the starting address of a list of storage addresses (e.g,. a TIDAL having multiple
TIDAWs) that make up the data utilized by the by the I/O operation. In exemplary
embodiments, the data is customer data (e.g., data input or output from the I/O operation).
In alternate exemplary embodiments, the data is control data (e.g., a TCCB). In an
exemplary embodiment, the list of storage addresses spans two or more non-contiguous
storage locations.
At block 1004, the data is gathered by instructions located at the channel subsystem 108.
The gathering is based on the contents of the list. In an exemplary embodiment, each entry
in the list (e.g., each TIDAW) includes both a storage address and a T-TIC flag to indicate
17
whether the storage address is the location of a portion of the data, or whether the storage
address points to the location of another portion of the list containing more storage
addresses. In this manner, a single TIDAL can be contained in multiple pages removing any
restraints on the length of the TIDAL. When the T-TIC flag indicates that the storage
address is the location of a portion of the data (e.g., the T-TIC flag is not set), then the data
at the storage location is accessed and added to the data. This adding of new data can be
performed in any manner known in the art, such as merging with data already gathered,
appending to data already gathered, etc.
When the T-TIC flag indicates that the current storage address is the location of another
portion of the list, then processing continues by accessing a new TIDAW located at the
specified storage location. Data at the storage location specified in the new TIDAW is
accessed and added to the data. In an exemplary embodiment, the TIDAW includes a count
904 to specify how much data to read (or write) from each storage address. When a TIDAW
with the last TIDAW flag is set the gathering is completed. Otherwise, the next TIDAW is
accessed and the data gathering continues.
At block 1006, the data is transmitted to a control unit 110 by the channel subsystem 108.
Technical effects of exemplary embodiments include providing non-contiguous indirect data
addressing at a I/O subsystem. By allowing multiple 4k byte pages to contain the list of
storage addresses (TIDAL) allows the number of TIDAWs to be unlimited, therefore more
data can be associated with a single I/O operation. Large transfers of data can reduce
communication overhead by avoiding additional handshaking and other delays associated
with multiple smaller messages.
The following examples depict manners in which exemplary embodiments may be utilized
to perform more than moving large blocks of data.
Exemplary embodiments may be utilized to aid in the prefixing of a channel program by an
operating system. For example, when a channel program is passed to an operating system,
the operating system may modify the channel program to add, replace, or modify command
CCWs or DCWs. In an exemplary embodiment, this implies that a TCCB TIDAL will be
created where the first TIDAW points to an area of storage containing the first part of the
modified TCCB. The second TIDAW points to the remainder of the unmodified TCCB.
18
Exemplary embodiments may also be used to aid in the prefixing of channel programs by a
hypervisor. If the hypervisor needs to modify the channel program, it would need to create a
TIDAL with one more entry than the one passed by the guest. If the TIDAL passed by the
guest is already the maximum size (256 TIDAWs), then the hypervisor can make its own
modifications by creating a TCCB TIDAL that has two TIDAWs, one of which is the TTICs
to the first TIDAW of the TIDAL passed by the guest.
TIDAL T-TICs can also ease storage requirements for operating systems. If the channel
program containing a TCCB TIDAL needs to be modified, it takes less storage to create a
TIDAW and T-TIC than to allocated storage for the caller’s TCCB TIDAL plus one more
TIDAW.
As described above, embodiments can be embodied in the form of computer-implemented
processes and apparatuses for practicing those processes. In exemplary embodiments, the
invention is embodied in computer program code executed by one or more network
elements. Embodiments include a computer program product 1100 as depicted in FIG. 11
on a computer usable medium 1102 with computer program code logic 1104 containing
instructions embodied in tangible media as an article of manufacture. Exemplary articles of
manufacture for computer usable medium 1102 may include floppy diskettes, CD-ROMs,
hard drives, universal serial bus (USB) flash drives, or any other computer-readable storage
medium, wherein, when the computer program code logic 1104 is loaded into and executed
by a computer, the computer becomes an apparatus for practicing the invention.
Embodiments include computer program code logic 1104, for example, whether stored in a
storage medium, loaded into and/or executed by a computer, or transmitted over some
transmission medium, such as over electrical wiring or cabling, through fiber optics, or via
electromagnetic radiation, wherein, when the computer program code logic 1104 is loaded
into and executed by a computer, the computer becomes an apparatus for practicing the
invention. When implemented on a general-purpose microprocessor, the computer program
code logic 1104 segments configure the microprocessor to create specific logic circuits.
While the invention has been described with reference to exemplary embodiments, it will be
understood by those skilled in the art that various changes may be made and equivalents may
be substituted for elements thereof without departing from the scope of the invention. In
addition, many modifications may be made to adapt a particular situation or material to the
19
teachings of the invention without departing from the essential scope thereof. Therefore, it
is intended that the invention not be limited to the particular embodiment disclosed as the
best mode contemplated for carrying out this invention, but that the invention will include all
embodiments falling within the scope of the appended claims. Moreover, the use of the
terms first, second, etc. do not denote any order or importance, but rather the terms first,
second, etc. are used to distinguish one element from another. Furthermore, the use of the
terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at
least one of the referenced item.
20
We Claim:
1. A method for providing indirect data addressing at an I/O subsystem of an I/O
processing system, the method comprising:
receiving a control word for an I/O operation at the I/O subsystem, the control word
including an indirect data address for data associated with the I/O operation, the indirect data
address including a starting location of a list of storage addresses that collectively specify the
data, the list spanning two or more non-contiguous storage locations;
gathering the data responsive to the list; and
transmitting the gathered data to a control unit in the I/O processing system;
wherein the list further includes a flag associated with each storage address in the list,
the flag having a first value to indicate that the associated storage address refers to a portion
of the data and the flag having a second value to indicate that the associated storage address
refers to a storage location where additional storage addresses in the list are located; and
wherein for each storage address on the list, the gathering includes:
accessing the storage address and the flag associated with the storage address;
adding contents from the storage address to the data in response to the flag having the
first value; and
accessing a second storage address and a second flag located at the storage address in
response to the flag having the second value, and adding contents from the second storage
address to the data in response to the second flag having the first value.
2. The method of claim 1 wherein a second storage address in the list is located
contiguously to a first storage address in the list when the flag has the first value, and the
second storage address is located non-contiguously to the first storage address when the flag
has the second value.
3. The method of claim 1 wherein the list further includes a count field associated with
each storage address in the list, the count field indicating a number of bytes to read from the
21
storage address and the gathering is responsive to the count fields and to the storage
addresses.
4. The method of claim 1 wherein the data includes control data.
5. The method of claim 1 wherein the data includes customer data.
6. The method of claim 1 wherein the control word is a transport control word (TCW),
the list of storage addresses is a transport indirect data address list (TIDAL), and each
storage address is a transport indirect data address word (TIDAW).
7. The method of claim 1 wherein the I/O subsystem is a channel subsystem.
8. The method of claim 1 wherein the control word includes a flag to indicate that it
includes an indirect data address.
9. A system comprising means configured for carrying out all the steps of the method
according to any preceding claims 1 to 8.


Dated this 27th day of March , 2010


P.H.D. RANGAPPA
OF K&S PARTNERS
AGENT FOR THE APPLICANT

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=0vX6Sh9yIPMD5amy6eweDw==&loc=egcICQiyoj82NGgGrC5ChA==


Patent Number 280019
Indian Patent Application Number 1751/CHENP/2010
PG Journal Number 06/2017
Publication Date 10-Feb-2017
Grant Date 07-Feb-2017
Date of Filing 27-Mar-2010
Name of Patentee INTERNATIONAL BUSINESS MACHINES CORPORATION
Applicant Address New Orchard Road, Armonk, NY 10504, USA
Inventors:
# Inventor's Name Inventor's Address
1 DANIEL CASPER 13 Brett Place, Poughkeepsie, New York 12603, United States of America.
2 JOHN FLANAGAN 15 Slate Hill Drive, Poughkeepsie, New York 12603, United States of America.
3 HARRY YUDENFRIEND 1 Nob Hill Road, Poughkeepsie, New York 12603-5545, United States of America.
4 MATTHEW KALOS 5435 East Heatherwood Way, Tucson Arizona 85718, United States of America.
5 MARK BENDYK 29 Hudson Drive, Hyde Park New York 12538, United States of America.
6 GUSTAV III SITTMANN 422 South Park Avenue, Webster Groves Missouri 63119, United States of America.
7 CATHERINE HUANG 6 Thornberry Way, Poughkeepsie New York 12603, United States of America.
8 DALE RIEDY 6 Oak Bend Road, Poughkeepsie, New York 12603, United States of America.
9 UGOCHUKWU NJOKU 426 Midland Avenue, Yonkers, New York 10704, United States of America.
PCT International Classification Number G06F 13/10
PCT International Application Number PCT/EP2009/051485
PCT International Filing date 2009-02-10
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 12/031,038 2008-02-14 U.S.A.