Multiple processor system having software for selecting shared cache entries of an associated castout class for transfer to a DASD with one I/O operation

• US 5,493,668 A
• Filed: 03/30/1992
• Issued: 02/20/1996
• Est. Priority Date: 12/14/1990
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Elko, David A., Strickland, Jimmy P., Narang, Inderpal S., Nick, Jeffrey M., Swanson, Michael D., Frey, Jeffrey A., Mohan, Chandrasekaran
• Primary Examiner(s): Lee, Thomas C.
• Assistant Examiner(s): WEINSTEIN, MARC
• Application Number:
  US07/860,806
• Time in Patent Office: 1,422 Days
• Field of Search: 395/425, 395/275, 395/250, 395/200, 364/200
• US Class Current: 711/130
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/084 with a shared cache
• CPC Class Codes: G06F 12/0868 Data transfer between cache memory and other subsystems, e.g. storage devices or host systems
• CPC Class Codes: G06F 12/128 adapted to multidimensional cache systems, e.g. set-associative, multicache, multiset or multilevel

Abstract

A high-speed cache is shared by a plurality of independently-operating data systems in a multi-system data sharing complex. Each data system has access both to the high-speed cache and the lower-speed, secondary storage for obtaining and storing data. Management logic and the high-speed cache assures that a block of data obtained form the cache for entry into the secondary storage will be consistent with the version of the block of data in the shared cache with non-blocking serialization allowing access to a changed version in the cache while castout is being performed. Castout classes are provided to facilitate efficient movement from the shared cache to DASD.

Claims

1. A method of controlling data transfer from shared storage to I/O devices in a computer complex, comprising the steps of:

structuring a sysplex to include a plurality of central processor complexes (CPCs), in which the CPCs use I/O control software for controlling sysplex direct access storage devices (sysplex DASDs) connected using first data paths to the CPCs for storing data items permanently in the sysplex, and a shared electronic storage (SES) connected using second data paths to the CPCs, wherein said first data paths are separate and distinct from said second data paths, in which the CPCs use SES control software for controlling SES over said second data path,

designating by said SES control software castout classes for SES cache directory entries to associate the castout classes with changed data items represented by the directory entries for enabling transfer to DASD in a single I/O operation of a plurality of data items selected from a castout class.

2. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 1, comprising the step of:

associating, using said I/O control software for controlling sysplex DASDs, castout classes designated for SES cache directory entries with identifications of sysplex DASD for locating a DASD for receiving a potential castout of data items associated with a respective castout class.

3. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 1, comprising the steps of:

associating a castout lock representation with each SES cache directory entry for a data item stored in a SES cache data area, and

setting the castout lock representation to a castout or non-castout state, in which the non-castout state has a predetermined value, and the castout state has a different value identifying a castout process used for transferring the associated data item to DASD.

4. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 3, the method further comprising the step of:

setting an indicating means for any valid SES cache directory entry to indicate a version of an associated data item stored in SES has been changed during a castout of the data item to DASD and the SES data item is not to be deleted from SES as long as the SES version is different from a version of the same data item stored in a sysplex DASD.

5. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 4, while the castout lock representation has the predetermined value indicating no castout state exists, the method further comprising the step of:

providing a change flag field in each directory entry in which the change flag field indicates whether or not an associated data item is stored in the SES cache with a version different from a version of the same data item stored in a sysplex DASD.

6. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 5, comprising the step of:

inhibiting reclaiming of a SES cache directory entry in a castout class when the change flag field indicates a different version is stored in the SES cache.

7. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 3, comprising the step of:

inhibiting reclaiming of a SES cache directory entry in a castout class when the castout lock representation indicates a castout state exists for the entry.

8. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 3, while the castout lock representation indicates a castout state exists and the change flag field indicates a changed state, the method further comprising the step of:

setting the change flag field to its non-changed state when the castout lock representation is set to provide a combinatorial indication (combining the indications for the change flag field and castout lock representation) indicating that a changed state exists for the version of the data item in the SES cache in relation to a DASD version of the same data item.

9. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 1, comprising the steps using said SES control software of:

counting entries in each castout class, and

initiating a castout process for a castout class when the number of SES cache directory entries counted for the castout class has reached a predetermined threshold number.

10. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 9, comprising the step of:

providing a counter means for each castout class which is incremented by each CPC write command specifying a castout class and writing a new data item in the castout class in SES, for which the counter means provides a measurement of the number of SES data items currently existing in each castout class.

11. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 10, comprising the steps of:

signalling by a timer program of the expiration of each time interval used for indicating the number of changed data items in each castout class currently measured by each castout-class counter means in a SES cache,

performing a measurement operation for measuring the number of changed data items currently existing in each castout class in a SES cache in response to a signal by the signalling step, and

initiating a castout process for any castout class which has the changed number of SES cache directory entries indicated by the measurement operation as equal to or exceeding a predetermined threshold number for the castout class.

12. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 10, comprising the steps of:

issuing of a write command by a CPC to a SES cache specifying a castout class for a data item, and

responding to the CPC command by SES sending a count of the number of data items stored in the specified castout class in the SES cache and the total number of data items in all castout classes in the SES cache.

13. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 1, comprising the steps of:

transmitting by a CPC to a SES cache of a command containing a name, a data item, a changed state indication, and a castout class for the data item,

accessing a directory entry in the SES cache having the name of the data item, and

setting in the directory entry a change flag field to the changed state indication for the data item, and setting a castout class field to the castout class for the data item being stored in SES regardless of whether a castout class was previously designated in the entry as changed or non-changed for the data item.

14. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 13, comprising the steps of:

transmitting a read-castout-class command from a CPC to a SES cache specifying a castout class,

accessing in SES of the queue for the castout class, and

finding a data item having a representation in the castout class.

15. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 14, comprising the steps of:

transmitting with the command of a name and a name mask to represent a set of related names potentially in the directory,

finding one or more names in a set defined by the mask applied to the name in a specified castout class, and

sending by SES to the CPC issuing the command of a list containing the set of names obtained by the finding step to inform the CPC of specific names in the castout class.

16. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 15, comprising the step of:

ordering the names found by the finding step in a recency of write-access sequence, and the sending step sending to the CPC the list of names in the recency of write-access sequence.

17. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 15, comprising the step of:

also sending by SES to the CPC of a count of the number of data items currently in the list being sent.

18. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 1, comprising the steps of:

transmitting a read-castout-class-information command from a CPC to a SES cache for requesting values in a set of counters accumulated in SES for respective predefined events occurring in relation to castout classes to enable the CPC to control a castout operation, and

responding by SES to the command by sending to the CPC of current values in the counters requested by the command.

19. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 1, comprising the steps of:

transmitting a read-directory command from a CPC to a SES cache for requesting information on one or more named data items,

scanning the entries in the SES cache directory for entries indicating a changed data item in SES (changed entries) for generating a name list or a list of directory-entry-information-blocks without being affected by changes to directory entries during the scanning step, and

responding to the command by SES sending to the CPC the name list or the list of directory-entry-information-blocks.

20. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 19, the responding step further comprising:

specifying a name and name mask in a read-directory command to define a set of related names for the scanning step to find entries in the directory for generating the name list or the list of directory-entry-information-blocks.

21. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 19, the responding step further comprising:

providing in each directory-entry-information-block for an associated data item of;

the name, change state, castout class, and castout lock state found in the directory entry for the data item.

22. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 1, further comprising the steps of:

transmitting by a CPC to a SES cache of a read-for-castout command containing a name of a data item being requested for castout,

testing in a directory entry in the SES cache for the name in the command, for a non-locked state in a castout lock field, and for a changed state indication for an associated data item, and

setting in the directory entry (when the conditions stated for the testing step are found) of the castout lock field to identify a castout process, the change field to indicate a non-changed state for the data item, and transmitting the data item to the CPC for the LCB.

23. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 22, further comprising the step of:

responding with a copy of the castout lock field and without transmitting the associated data item to the CPC when the castout lock field indicates a locked state.

24. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 23, further comprising the steps of:

transmitting by a CPC to a SES cache of a unlock-castout-locks command containing a list of one or more names of data items being requested for unlocking,

comparing an identifier of the CPC sending the command with a CPC identifier in a castout lock field for each directory entry found for a name in the list, and

accepting the command by resetting the castout lock field to a predetermined value indicating an unlocked state if the comparing step finds equality, but rejecting the command without changing the castout lock field if the comparing step finds inequality.

25. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 24, further comprising the step of:

forcing a change field in a directory entry to indicate a changed state for an associated data item if a requested castout operation for the data item is unsuccessful.

26. A method of controlling data transfer to I/O in a computer complex as defined in claim 24, further comprising the step of:

responding with a list locator representation when a rejection of a command occurs for a name in the list to enable the CPC to recognize it need not castout the data item, or to later again request a castout of the data item.

27. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 22, further comprising the step of:

registering an LC identifier (when registration is selected by the program) to indicate the local cache buffer used to store the data while in transit to DASD, to affect a read and register operation to the local cache and a castout operation in a single data transfer from SES to the CPC.

28. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 22, further comprising the steps of:

suppressing registration of an LCB identifier (when suppression of registration is selected by the program) to allow the castout operations to bypass the local-cache buffers.

29. A method of controlling data transfer to I/O in a computer complex as defined in claim 1, further comprising the steps of:

transmitting by a CPC to a SES cache of a command containing a name for finding any SES directory entry having the same name associated with a data item stored in the SES cache, and

putting a representation of the directory entry at an end of a castout queue for the castout class designated for the associated data item, the representation being put at a most recently changed (MRC) end of the queue to have the queue order its representations in recency order of data items changed in the castout class, with the least recently changed (LRC) data item in the castout class being indicated at the opposite end of the queue.

30. A method of controlling data transfer to I/O in a computer complex as defined in claim 29, further comprising the step of:

providing a write command as the command referencing a directory entry having a representation in the castout class.

31. A method of controlling data transfer to I/O in a computer complex as defined in claim 30, further comprising the step of:

providing a write and register command or a write when registered command referencing a directory entry having a representation in the castout class.

32. A method of controlling data transfer to I/O in a computer complex as defined in claim 30, further comprising the steps of:

rejecting the write command if the command represents a no-change state for a transmitted data item and a directory entry is found for the name of the data item in the command which indicates a changed state, and

responding to the CPC issuing the command with a rejection signal indicating the command is incompatible with the change state in the directory entry.

33. A method of controlling data transfer from shared storage to I/O devices in a computer complex, comprising the steps of:

structuring a sysplex to include a plurality of central processor complexes (CPCs), in which the CPCs use I/O control software for controlling sysplex direct access devices (sysplex DASDs) connected to the CPCs for storing data items permanently in the sysplex, and a shared electronic storage (SES), in which the CPCs use SES control software for controlling the SES,

designating by said SES control software castout classes for SES cache directory entries to associate the castout classes with changed data items represented by the directory entries for enabling transfer to DASD in a single I/O operation of a plurality of data items selected from a castout class,

associating a user-data field with each SES cache directory entry in which to indicate the time of initially writing an associated data item in the SES cache, and

writing a time in the user-data field when a change flag field is set in the directory entry to indicate that the associated data item is different from a copy of the same data item in the sysplex DASD.

34. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 33, the writing step further comprising:

using the user-data field to control backup by indicating a time from which backup is needed in case of failure of the SES cache.

35. A method of controlling data transfer from shared storage to I/O devices in a computer complex as defined in claim 33, the detecting step further comprising:

retrieving by a CPC of the time of change of a data item in a user-data field of a SES directory entry to reduce recovery time for a SES cache after failure of the SES cache.