Monitor 7
8 SEEKS SYSPROF Data Collection Function collects-aita -for-every I/O request to DASD. Reveals channel, control unit, or device
contention and arm movement interference
Note: When VIrtual=real collected. NOTRANS machine,
is in effect
no meaningful
No data is collected for TIO or HIO operations.
For SIO operations, data is collected when the
request for the I/O operation is initially
handled and again when the request is
This means that a single SIO request could
result in two MONITOR CALLs. For example, if
the request gets queued because the device is
already busy, then a MONITOR CALL would be
issued as the request is queued. Later, when
the device becomes free and is restarted, a
second MONITOR CALL is issued.
In general, the data collected is the same
except that in the first case there will be
nonzero counts associated with queued requests.
If the request for I/O is satisfied when it is
initially handled without being queued, only
one MONITOR CALL results. In both this case
and the second of the two data collections
mentioned above, the count of I/O requests
queued for the device is zero.
Collects data complementary to the DASTAP and SCHEDULE classes in order to provide a more
detailed "profile" of system performance
through a closer examination of DASD utilization. VM/370 MONITOR RESPONSE TO UNUSUAL TAPE CONDITIONS When I/O to the tape is requested, the device may still be busy from the
previous request. If this occurs, two data pages are full and data
collection must be temporarily suspended. Control register 8 is saved
and then set to zero to disable MONITOR CALL program interruptions and timer data collection. A running count is kept of the number of times
suspension occurs. The current Monitor event is disregarded. When the
current tape I/O operation ends, the next full data page is scheduled
for output. MONITOR CALL interruptions are reenatled (control register 8
is restored), a record containing the time of suspension, the time of
resumption, and the suspension count is recorded and data collection
continues. The suspension count is reset to zero when the MONITOR STOP TAPE is issued. Part 2. Control Program (CP) 121
When an unrecoverable error occurs, DMKMON receives control and attempts to write two tape marks, rewind, and unload the tape. The use of the
tape is discontinued and data collection stops. The operator is informed
of the action taken. Whether or not the write-tape-marks, rewind, and
unload are successful, the tape drive is released. When an end-of-tape condition occurs, DKKMON receives control. A tape
.ark is written on the tape and it is rewound and unloaded. The VM/310 Monitor is stopped and the operator is informed of the action taken. VM/310 MONITOR CONSIDERATIONS The system programmer may want to set the TRACE(1} bit to a 1 in the LOCAL COpy file and reassemble DMKMCC to allow RESPONSE data (MOIITCH class 1) to be collected. See the information about security exposure
in "MONITOR ENABLE Restrictions" in the MONITOR command description. MONITOR START CPTRACE is active after real system IPL (manual or
automatic). The VM/370 Monitor tape data collection is off after IPL. If automatic performance monitoring is specified in the SYSMON macro and
IPL occurs within the range of the TIME operand of the 5YS80N macro. VM/370 monitor data collection to a spool file is started.
If the VM/370 Monitor data collection to a spool file is taking place, a
system shutdown causes closing of the file and termination of
monitoring. If data collection is to tape, a system shutdown implies a MONITOR STOP TAPE command. Normal command processing for the MCIITOS STOP TAPE function is performed by the If the VM/370 system fails and data collection to a spool file is
active, the spool file is closed and preserved, except for the last
buffer. If the VM/370 system fails and data collection is active on
tape, an attempt is made to write two tape marks, rewind, and unload the
tape. If the tape drive fails to rewind and unload, be sure to write a
tape mark befere rewinding and unloading the taFe. VM/370 Monitor data
collection is terminated by the system failure.
122 IBM System Programmer's Guide
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