The MONITOR Command VM/370 Monitor collects data in two ways:
1. By handling interruptions caused by executinq MONITOR CALL (MC) instructions.
2. By usinq timer interruptions to
sampling-routines. rriuo :;,--- periodically to MONITOR CALL instructions with appropriate classes and codes are
presently embedded in strategic places throughout the main body of VM/370 code (CP). When a MONITOR CALL instruction executes, a program interruption occurs if the particular class of ftONITOR CALL is enabled.
The classes of MONITOR CALL that are enabled are determined by the mask
in control register 8. For the format and function of the MONITOR CALL
instruction, refer to the of The
format of control register 8 is as follows:
1 I I I I I I I I xxxx xxxx xxxx xxxx 0123 4567 89AB CDEF I I I I I I I I I x indicates unassigned bits. O-F (hexadecimal)
indicates the bit associated with each class of
the MONITOR CALL. When a MONITOR CALL interruption occurs, the CP proqram interruption
handler (DMKPRG) transfers control to the VM/370 Monitor interruption
handler (DMKMON) where data collection takes place.
Sixteen classes of separately enabled MONITOR CALL instructions are
possible, but only eight are implemented in the VM/370 Monitor. Monitor output consists of event data and sampled data. Event data
is obtained via MONITOR CALL instructions placed within the VM/370 code.
Sampled data is collected following timer interruptions. All data is
recorded as though it were obtained through a MONITOR CALL instruction.
This simplifies the identification of the records.
The following table indicates the type of collection mechanism for
each Monitor class:
Monitor Class Collection Mechanism 0 PERFORM rIier-requests 1 RESPONSE MC instructions
2 SCHEDULE MC instructions
3
1
4 USER Timer requests
5 INSTSIM MC instructions
6 DASTAP Timer requests
7 SEEKS MC instructions
8 SYSPROF Collected via class 2 IThere is no class name for monitor class 3, but it is reserved. 110 V!/370 System Guide

Page of GC20-1807-7 As Updated April 1, 1981 by TNL GN25-0829 Another function, separate from the VM/370 Monitor, is also handled uy the MONITOR command. The MONITOR command can stop and start CP
internal trace table data collection, which is initiated by MONITOR CALLs.
Note: The VM/370 Monitor record format and the contents of the record
are shown in "Appendix C. Monitor Tape Format and content ...
The MONITOR command: • stops and starts CP internal trace table data collection. • Displays the status of the internal trace table and each implemented
class of VM/370 Monitor data collection. Displays the specifications
for automatic monitoring defined by the SYSMON macro in DMKSYS. In
addition, it displays those specifications for automatic monitoring
that are overridden by Monitor commands. It also the tape, or spool file is the recording medium. • starts and stops VM/370 data collection using tape or spool filee It
also closes the spool file, if desired. • specifies VM/370 monitor classes of data collection enabled, number
of buffers used, and time of data collection. It also specifies
other options which override the specifications for automatic
monitoring on the SYSMON macro contained in DMKSYS. • Specifies the interval to be used for timer driven data collection. • specifies direct access devices that are to be
from a list of devices. The list defines direct
which CP is to collect data for the SEEKs class.
included or excluded
access devices for Part 2. Control Program (CP) 111