6. DATA SOURCES › 6.6 I/O Measurements and Device Activity › 6.6.1 What Is an I/O? › 6.6.1.2 What Is and Is Not Counted as an I/O?

6.6.1.2 What Is and Is Not Counted as an I/O?

The I/O activities that are counted in the EXCP measure are:

  o EXCPs issued via an EXCP macro (SVC 0).

  o EXCPs issued via a TCBEXCP macro (SVC 92).

  o EXCPs issued via an EXCPVR macro (SVC 114).

  o EXCPs issued in a system or user-provided channel-end
    appendage.

  o EXCPs issued in an abnormal-end appendage.

  o I/O for VSAM data sets (SVC 121).

  o EXCPs for VIO data sets (even though no physical I/O may
    take place).

  o EXCPs issued to the SYSUDUMP, SYSABEND, and SYSMDUMP data
    sets when these data sets reside on a direct access or
    tape device.

  o I/O for some system services, for example:

    - JOBLIB/STEPLIB processing (i.e., I/O for program fetch)
    - JOBCAT/STEPCAT processing (i.e., I/O for program fetch)
    - Overlay supervisor processing
    - Checkpoint data set processing

The I/O actions that are NOT counted in the EXCP measure are:

  o EXCPs to any data set for which the memory has no (JCL or
    dynamic) DD entry (for instance, I/O to the Master
    Catalog or to load libraries in the LNKLST).

  o EXCPs issued in a PCI appendage for a memory running V=R
    (ADDRSPC=REAL).

  o EXCPs issued by ASM for paging and swapping.

  o EXCPs issued by IOS during error recovery.

  o EXCPs issued by OLTEP.

  o EXCPs issued on the address spaces' behalf by VTAM.

  o TPUTs and TGETs handled by macro instructions.  (For
    TPUTs and TGETs, EXCPs are accumulated on a system basis
    in the TCT and are contained in SMF type 30 records.)

  o If more data-sets are allocated during the step than are
    allowed for in the default TIOT, a GETMAIN is issued for
    a TIOT extension.  Because the TIOT is where the EXCP
    counts are maintained, if the GETMAIN fails, then only
    the data sets in the unextended TIOT contribute to the
    reported count.