Detail VMX Demand Scan Summary

Detail VMX Demand Scan Summary report produces a tabular listing of demand scan activity in time sequence.
micsrm140cd
The information is summarized by the number of minutes specified by the user as a run-time execution parameter. Activity is displayed over the time-frame specified by the user, again as run-time execution parameters.
Intended use
When CP needs additional storage to continue processing, it takes frames from the CP-maintained list of available frames. If CP cannot find a frame in the available list, it must take frames away from the virtual systems to replenish the available list. CP invokes a demand scan function to replenish the available list when it reaches a point called the low threshold. The function removes selected frames from user-owned frame lists, and places them on the available list. The demand scan function places frames on the available list until the list reaches a value called the high threshold. The demand scan function consists of two passes of various VMDBKs, and a special emergency pass if the two regular passes do not successfully replenish the list.
Within each pass, the function examines VMDBKs in an order that will hopefully have the least impact on a given user and on the system as a whole. For example, in the first pass of the function, long-term dormant users are examined first, followed by short-term dormant users. Next, the shared frame owned list (including system VMDBK, named saved systems, discontiguous saved segments, and shared address spaces) is examined for frames to remove, followed by the eligible list, and finally the dispatch list. With each succeeding pass, the function becomes less selective about which frames to take from users.
The VM Monitor records count indicating at which point in the demand scan function the available list was successfully replenished. For example, over a five-minute period, during an average interval, the Demand Scan function might complete after scanning the short-term dormant list in Pass 1, 90.0 times. This report indicates the average number of times per monitor interval that the demand scan function completed within a given phase of the function.
The report is intended to show how far into the Demand Scan function it is necessary to proceed before the available frame list is replenished. If numbers start appearing in the Emergency Pass part of the report, it can be indicative of a storage-constrained environment.
Format
A tabular report in chronological order, where each line represents a summarization of DETAIL data across a user-specified time-frame. The columns within each Demand Scan Pass represent the average number of times per monitor interval that the Demand Scan function completed in that phase. They are ordered from left to right in the same order that the system algorithm proceeds through the various lists of VMDBKs. The following abbreviations are used for column headings with each pass:
LTD
Long Term Dormant VMDBKs
STD
Short Term Dormant VMDBKs
SYS/SHAR
System VMDBK, Shared Storage VMDBKs (NSSs and DCSSs), and Shared Address Spaces
ELST
Eligible List VMDBKs
DLST
Dispatch List VMDBKs
The final three columns of the report show the following averages for the reporting interval (these are not totals):
SCAN NCMP
The average number of times per monitor interval that the Demand Scan Function did not complete successfully.
ALIST EMPTY
The average number of times per monitor interval that the available frame list was empty.
DFRD TASKS
The average number of tasks per monitor interval that were deferred while waiting for a page of real storage. This represents the average number of requests for real frames that have not been satisfied yet because no frames are available.
An example of this report is shown in the Detail VMX Demand Scan Summary figure.
Inquiry ID
  • Tabular Report: VMXTX4
Data Source (File/Timespan):
VMXSPP01 - DETAIL
Data elements used
SPPLD1CT
- DScan Pass 1 Complete Long Term Dormant
SPPDM1CT
- DScan Pass 1 Complete Short Term Dormant
SPPSY1CT
- DScan Pass 1 Complete SYSTEM VMDBK (* note)
SPPSS1CT
- DScan Pass 1 Complete Shared Frame Owned List
SPPEL1CT
- DScan Pass 1 Complete Eligible List
SPPDL1CT
- DScan Pass 1 Complete Dispatch List
SPPLD2CT
- DScan Pass 2 Complete Long Term Dormant
SPPDM2CT
- DScan Pass 2 Complete Short Term Dormant
SPPEL2CT
- DScan Pass 2 Complete Eligible List
SPPDL2CT
- DScan Pass 2 Complete Dispatch List
SPPSSECT
- DScan Pass E Complete Shared Frame Owned List
SPPDMECT
- DScan Pass E Complete Short Term Dormant
SPPELECT
- DScan Pass E Complete Eligible List
SPPSYECT
- DScan Pass E Complete SYSTEM VMDBK (* note)
SPPDLECT
- DScan Pass E Complete Dispatch List
SPPNOCMP
- Demand Scan Not Completed Successfully
SPPALMPT
- Times Available List Became Empty
SPPFRQWT
- Deferred Tasks Waiting for A Frame
Note:
SPPSY1CT and SPPSYECT are only applicable to systems prior to VM/ESA Release 2.
Calculations
The various elements to be reported on are summarized across processors, using
MICS
summarization, to provide system-wide totals.
MICS
summarization is then invoked a second time to summarize across the user-specified time period, if necessary. Finally, before reporting, each element is averaged by dividing it by the number of monitor intervals.
Usage considerations
To obtain a detail report, with one line per monitor interval, specify 0 for the Summarization Period in the run-time execution parameters.

Detail VMX Demand Scan Summary Sample

+----------------------------------------------------------------------------------------------------------------------------------+ | Detail VMX Demand Scan Summary | |
Broadcom
I/S MANAGEMENT APPLICATIONS DEVELOPMENT | | | |INQUIRY: VMXTX4 RUN DATE: 15MARyy | | System ID = VM01 Date = Wednesday, February 10, yyyy | |----------------------------------------------------------------------------------------------------------------------------------| | DEMAND SCAN PASS 1 DEMAND SCAN PASS 2 DEMAND SCAN EMERGENCY PASS SCAN | | -------------------------------- ---------------------- --------------------------- NOT ALIST DEFRD | | TIME LTD STD SYS/SHAR ELST DLST LTD STD ELST DLST SYS/SHAR STD ELST DLST CMPL EMPTY TASKS | |----------------------------------------------------------------------------------------------------------------------------------| |12:25:00 14.0 0.0 0.0 0.0 3.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 56.0 | |12:30:00 28.4 0.0 0.0 0.0 2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 7.0 80.0 | |12:35:00 54.7 0.0 0.7 0.0 7.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.3 149.3 | |12:40:00 79.5 0.0 0.0 0.0 9.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 5.5 288.0 | |12:45:00 89.0 0.0 0.5 0.0 9.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.5 264.0 | | | | | | | | | | | | | | | | | +----------------------------------------------------------------------------------------------------------------------------------+