OA44109: HIGH CPU RASP GLOBAL STEAL SCM

Obtain the fix for this APAR.

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 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
  

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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