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A fix is available


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APAR status

  • Closed as program error.

Error description

  • During periods where CSM fixed storage is constrained, TCP
    outbound processing fails during send processing trying to
    extend BGRPs. The BGRP is used for outbound blocking and
    allocation attempts for new BGRPs fails when CSM fixed is
    constrained. This causes BGRPs to be leaked in ECSA, but this
    leak also causes 32k fixed CSM dataspace buffers associated
    with these leaked BGRPs to accumulate. This accumulation of CSM
    fixed storage causes CSM to remained constrained for long
    periods of time. When CSM becomes constrained all outbound and
    inbound packet operations can fail, resulting in degraded
    performance and eventually connection failures.  Running in a
    constrained mode for a lengthy period of time will result in
    total failure of the stack operations and most likely will
    result in an IPL.
    Additional Symptom(s) Search Keyword(s): BGRP CSM fixed 32k
    dataspace CSM64001

Local fix

  • enable segmentation offload or increase CSM fixed storage if
    real memory is not a factor
    Verification steps:
    The orphaned BGRP control blocks in ECSA will have the
    - offset x'14'  will have x'66'
    - offset x'CC' will be an address to an SKMB/SKDB  that points
       to the orphaned CSM 32k dataspace fixed buffer
       the SPAC at offset x'F0' into the BGRP has a zero
       SPAC_WE_NEXT (offset 4) value
    - There will be a high number of CSM 32k DATASPACE buffers with
      a CSM Monitor ID value of x'92' (ifBlockPack) owned by
    - CSM storage displays will show CSM fixed storage owned by
       TCPIP increasing as well as CSM constrained message IVT5592I
       and IVT5565I periodically
    -  SYSTCPIP VTAMDATA exception records:
       " !Storage Error - Msg_Wont_Fit"     and
       " !Storage Error on BGRP" will be seen

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All users of the IBM Communications Server   *
    *                 for z/OS Version 1 Release(s) 12 and 13 IP   *
    * PROBLEM DESCRIPTION: CSM FIXED ECSA and dataspace storage    *
    *                      leak when CSM is in the constrained or  *
    *                      critical state                          *
    * RECOMMENDATION:                                              *
    Fixed CSM ECSA and dataspace storage leak when CSM is in the
    constrained or critical state.
    A blocking algorithm is used to acheive optimal performance
    when sending packets outbound over an OSA device.  The blocking
    process uses a control structure that resides in fixed CSM ECSA
    and a 32K buffer that resides in fixed CSM dataspace.  When TCP
    connections are streaming large amounts of data outbound it can
    result in the need for multiple blocking control structures and
    32K buffers.  The allocation of additional control structures
    and 32K buffers fail when CSM is in a constrained or critical
    state for fixed storage.  When an allocation failure for the
    control structure or 32K buffer fails and two or more already
    exist for the device, the last control structure and 32K buffer
    successfully allocated for the device will be leaked.
    Enabling segmentation offload on the IPCONFIG, IPCONFIG6, or
    GLOBALCONFIG profile statements can be used to optimize the
    CPU utilization for outbound TCP traffic and prevents this
    problem from occurring.
    + Please check our Communications Server for OS/390 homepages +
    + for common networking tips and fixes.  The URL for these    +
    + homepages can be found in Informational APAR II11334.       +

Problem conclusion

  • EZBIFBP1 has been amended to handle the allocation failure of
    a blocking algorithm control structure or 32K buffer.
    * Cross Reference between External and Internal Names

Temporary fix

  • *********
    * HIPER *


APAR Information

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  • Reported component name


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  • PE




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

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

    UK91704 UK91706



Fix information

  • Fixed component name


  • Fixed component ID


Applicable component levels

  • R1C0 PSY UK91704

       UP13/04/11 P F304

  • R1D0 PSY UK91706

       UP13/04/11 P F304

Fix is available

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Document information

More support for: z/OS family

Software version: 1D0

Operating system(s): z/OS

Reference #: PM81034

Modified date: 06 May 2013