6. DATA SOURCES › 6.3 VM Monitor Data

6.3 VM Monitor Data

VM CP Monitor facility collects system performance data and
stores it in the saved segment.  An application program (such
as the IBM MONWRITE program) is used to establish
communication links with CP, retrieve monitor records, and
stores them in a sequential file on disk or on tape.

The MONWRITE output contains control records and monitor data
records.  The sequence of records is one 4KB control record,
the monitor data records associated with that control record,
the next 4KB control record, the monitor data records, and so
forth, until the last record is a 4KB end-of-data record.

Each 4KB control record describes the monitor data stored
immediately after this record in the output file.  It
contains a IUCV message pending interrupt buffer and the
control area which contains one or more control area entries.
Each control area entry contains the addresses of the first
byte and the last byte of monitor data.  The format of the
control record follows.

    MWTEXTBF  DS  XL40    Message pending interrupt buffer
    MWTCAREA  DS  XL4056  Control area
              ORG MWTCAREA
    MWTCADOM  DS  F       Domain information
    MWTCASTR  DS  F       Data start address
    MWTCAEND  DS  F       Data end address

There are two types of VM monitor data:  event data and
sample data.

Event data is collected and reported each time a designated
system event occurs.  It represents the status of the system
at the time the event occurred.

Sample data is collected and reported at the end of each
designated time interval.  Sample data contains single sample
data and high frequency sample data.

  o Single sample data is collected once during the time
    interval, and only at the end of that time interval.

    Single sample data represents the status of the system at
    the time the data was collected.  It is an accumulation
    of counters, states, or elapsed times collected at the
    end of each time interval since sampling started.

  o High frequency sample data is collected several times
    during the time interval, but reported along with single
    sample data.

    High frequency sample data is a set of counters and data
    that represent the state of the system at the moment the
    system is sampled.

Each monitor record contains a header which identifies the
record and when it was built.  These fields are:

    MRHDRLEN DS   H     Record descriptor word
             DS   H
    MRHDRDM  DS   X     Domain
             DS   X     (reserved)
    MRHDRRC  DS   H     Record type
    MRHDRTOD DS   D     Record timestamp in Time-of-Day clock
                        format
             DS   4X    (reserved)

CP places as many monitor records as possible into a 4K
segment space.

The VM Data Transfer Program strips the control records from
MONWRITE output and reformats the data into variable record
format for processing by the CA MICS VM and CMS Analyzer.