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OA44109: HIGH CPU RASP GLOBAL STEAL SCM

A fix is available

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APAR status

  • Closed as program error.

Error description

  • On a system with SCM memory installed and no LFAREA specified
    the system is experiencing high cpu consumption in the RASP
    address space running the srb for global steal.  The system
    has very high demand for pageable 1meg frames which is causing
    high paging for these frames to SCM and high stealing and
    reform of these pageable 1meg frames when there is no fixed
    LFAREA to overflow the pageable 1meg demand into.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: Users of JBB778H and above                   *
    ****************************************************************
    * PROBLEM DESCRIPTION: High CPU consumption in RASP address    *
    *                      space occurs after a very high demand   *
    *                      for pageable 1meg frames.               *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    When the system detects that it is running low on pageable
    1meg frames, it schedules an SRB in the RASP address space
    to replenish the pageable 1meg area (PLAREA).  Detection
    is partially based on the number of failed attempts to
    back storage with a pageable 1meg frame since the last
    time the system experienced a 4k frame shortage (AVQLOW).
    
    The problem with this detection scheme is that the system
    can experience a very high demand for pageable 1meg frames
    without experiencing AVQLOW.  Therefore, the detection
    trigger may not get reset when the next pageable 1meg
    frame request is made.  This results in excessive
    scheduling of the SRB to replenish the PLAREA, which
    leads to high CPU consumption in the RASP address space.
    
    There are additional problems with unnecessary and undesirable
    scheduling of the SRB to replenish the PLAREA.
    
    The following is a list of unnecessary scheduling:
    - Scheduling the SRB to perform pageable 1meg coalescing
      when there are no pageable 1meg frames to coalesce
    - Scheduling the SRB to perform pageable 1meg paging
      when there are no pageable 1meg frames to page out
    
    The following is a list of undesirable scheduling:
    - Scheduling the SRB to perform pageable 1meg coalescing
      when there are not enough eligible 4K frames available
      above the bar OR the system is below RCEAFCOK
      (coalescing requires above the bar 4K frames,
      therefore it is not desireable to perform coalescing
      if the system is low on above the bar 4K frames
      or on 4K frames in general)
    - Scheduling the SRB to perform pageable 1meg paging
      when the system is above RCEAFCOK (paging, whether 4K
      or 1meg, should only be performed when the system is
      AVQLOW)
    
    Additional keywords:
    pageable large pages, pageable1meg, megabyte, 1M
    

Problem conclusion

  • Processing is changed to correct the detection scheme used
    to determine when to schedule the SRB that performs PLAREA
    replenishment.  The detection trigger will be reset every
    time the SRB is scheduled as opposed to only when AVQLOW
    occurs.
    
    Checks are added to eliminate the unnecessary and
    undesirable scheduling of the SRB that performs PLAREA
    replenishment, documented in the problem summary.
    
    Documentation Updates:
    ----------------------
    
    The information in the following z/OS manuals should appear as
    indicated below.  Updates will only be made to the manuals in
    future z/OS releases.
    
    -------------------------------------------------------------
     GA32-0857-XX JBB778H
     GA32-0939-XX HBB7790
     z/OS MVS Data Areas Volume 5
    -------------------------------------------------------------
    
      ---------------
      Section Titled:
      RCE Cross Reference
    
       Name                         Hex Offset  Hex Value
    |  RCEPLFAILEDSINCEPLARGESTEAL  3E8
    
      ---------------
      Section Titled:
      RCE Map
    
      Dec   Hex    Type/Value  Len  Name (Dim)  Description
    | 1000  (3E8)  UNSIGNED      8  RCEPLFAILEDSINCEPLARGESTEAL
    |                                Last count of total number of
    |                                failed attempts to back storage
    |                                with pageable large frames
    |                                (RCEPMMSS+RCENMMSS) since
    |                                Pageable Large Steal called
    
      ---------------
      Section Titled:
      RIT Cross Reference
    
       Name                         Hex Offset  Hex Value
    |  RITPLBITS                    656
    |  RITPLCOALESCEDONE            656         40
    |  RITPLCOALESCEINPROGRESS      656         10
    |  RITPLDOSTEAL                 656         80
    |  RITPLPAGINGDONE              656         20
    
      ---------------
      Section Titled:
      RIT Map
    
      Dec   Hex    Type/Value  Len  Name (Dim)  Description
      1622  (656)  BITSTRING     1  RITPLBITS
    |              1... ....         RITPLDOSTEAL
    |                                 Bit indicating that IAXUO
    |                                 should replenish the PLAREA
    |              .1.. ....         RITPLCOALESCEDONE
    |                                 Internally used (for unit or
    |                                 function test) to verify that
    |                                 replenishment by coalescing
    |                                 was done
    |              ..1. ....         RITPLPAGINGDONE
    |                                 Internally used (for unit or
    |                                 function test) to verify that
    |                                 replenishment by paging
    |                                 was done
    |              ...1 ....         RITPLCOALESCEINPROGRESS
    |                                 Indicates that coalescing is
    |                                 in progress (used by IAXUA to
    |                                 prevent 1M singles or groups
    |                                 from being used while
    |                                 coalescing is in progress)
    

Temporary fix

  • *********
    * HIPER *
    *********
    

Comments

APAR Information

  • APAR number

    OA44109

  • Reported component name

    RSM - REAL STOR

  • Reported component ID

    5752SC1CR

  • Reported release

    78H

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2013-12-13

  • Closed date

    2014-03-09

  • Last modified date

    2014-04-02

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

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

    UA72670 UA72671

Modules/Macros

  • IARRCE   IAXUA    IAXUO
    

Publications Referenced
GA320939XX GA320857XX      

Fix information

  • Fixed component name

    RSM - REAL STOR

  • Fixed component ID

    5752SC1CR

Applicable component levels

  • R78H PSY UA72671

       UP14/03/26 P F403 Ž

  • R790 PSY UA72670

       UP14/03/26 P F403 Ž

Fix is available

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Document information

More support for: z/OS family

Software version: 78H

Operating system(s): MVS, z/OS

Reference #: OA44109

Modified date: 02 April 2014