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PI56728: REDISPATCH WAIT TIME (DISPWTT) VALUE HIGHER THAN SUSPEND TIME (SUSPTIME) FOR SOME TRANSACTIONS

A fix is available

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APAR status

  • Closed as program error.

Error description

  • You see dispatch wait time (DISPWTT) is higher than the
    suspend time (SUSPTIME) for some transactions.
    
    This problem has been tracked to a problem updating the DISPWTT
    field during a TCB switch. These are different from normal
    suspends because you don't need to wait for a resource. In a
    normal suspend, we would pop the task off the TCB it is running
    on, suspend the task (and start the SUSPTIME clock). Then later
    the resource you are waiting for would become available. The
    task then gets made dispatchable, and put on the dispatchable
    chain of its TCB. We start the DISPWTT clock at this point.
    
    A change mode is different in that there is no real resource
    being waited for. The task is put onto the dispatchable queue
    of its new TCB right away, so all of the time for which it is
    "suspended" is time waiting for its new TCB. A problem with the
    way the calculation is performed for a TCB CHANGE_MODE  meant
    that the amount added to DISPWTT is actually very very slightly
    larger than the amount added to SUSPTIME. You would expect it
    would be exactly the same, or perhaps very very slightly
    smaller.
    
    This means that in a workload that does a very large number of
    TCB switches, relative to the amount of time spent in a 'real'
    suspend, it is possible for the DISPWTT time to catch up to,
    and overtake the SUSPTIME. I think a more normal workload with
    real suspends in it would never encounter this issue, and this
    is why it only hit it on certain transactions.
    
    
    Additional Symptom(s) Search Keyword(s): KIXREVSVR
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All CICS Users.                              *
    ****************************************************************
    * PROBLEM DESCRIPTION: Monitoring field DISPWTT can have       *
    *                      a value that is greater than the        *
    *                      SUSPTIME field value.                   *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    When performance monitoring is turned on, a task that is
    entering dispatcher due to a change tcb mode request or a change
    priority request will result in the amount added to the Dispatch
    Wait Time (DISPWTT) value being greater than the amount added to
    the Task Suspend Time (SUSPTIME).
    
    It is stated in the knowledge center that the SUSPTIME includes
    the value of the DISPWTT field. The DISPWTT field is calculated
    by noting the time when a task is made dispatchable and then
    using this with the dispatch start time to figure out how long
    the task was waiting to be dispatched. The dispatch start time
    is also used to stop the clock that records the SUSPTIME.
    However, the field used to note the time when the task is made
    dispatchable is not updated at this point and was last used just
    before the task suspended. This has resulted in the DISPWTT
    value being greater than the corresponding SUSPTIME.
    
    Additional Keywords: 014 102 ENQUEUE_TIME WAIT_FOR_REDISP
                         DISPATCH_START TMA_DFHTASK_014
                         TMA_DFHTASK_102
    

Problem conclusion

  • DFHDSTCB has been updated to ensure that ENQUEUE_TIME is updated
    when a task is made dispatchable for a change_mode or
    change_priority request.
    

Temporary fix

  • FIX AVAILABLE BY PTF ONLY
    

Comments

APAR Information

  • APAR number

    PI56728

  • Reported component name

    CICS TS Z/OS V4

  • Reported component ID

    5655S9700

  • Reported release

    600

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2016-02-05

  • Closed date

    2016-04-19

  • Last modified date

    2016-05-04

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

    PI59218 PI59219 UI37218 UI37219

Modules/Macros

  • DFHDSTCB
    

Fix information

  • Fixed component name

    CICS TS Z/OS V4

  • Fixed component ID

    5655S9700

Applicable component levels

  • R600 PSY UI37218

       UP16/04/28 P F604

  • R700 PSY UI37219

       UP16/04/28 P F604

Fix is available

  • Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.

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Document Information

Modified date:
04 May 2016