Reduce overhead associated with maintaining shadow page and segment
tables Improve Ferformance for a production virtual storage operating system
running under VM/370 Increase throughput of MVS running under VM/370 on an attached
Frocessor or multiprocessor system
For more details about this program product, refer to the GC20-1827. PERFORMANCE MEASUREMENTS Performance measurements apply to both the VM/370 system and the
individual virtual machine. How well the system responds to the needs
of the users is of prime importance to the system analyst. How
efficiently the individual virtual machine makes use of the allotted
storage, prccessor, and I/O facilities is of prime importance to the
general usera VM/370 Frovides certain CP commands (INDICATE and MONITOB) that allow beth VM/370 and virtual machine performance to be tracked and measured;
other commands allow the setting of certain options to improve
performance. To reduce and help analyze the data produced by the MONITOR command, the Field Developed program VM/370 Performance/Monitor
Analysis program (5748-CPX) is available. By using this program, an
installation can eventually determine its optimum processor model,
storage size, and I/O configuration for a specific workload.
Fer a comFlete description of the INDICATE and MCNITOR commands,
refer to the EMPHASIZING INTERACTIVE RESPONSE TIMES Most conditions for good performance, established for the time-sharing
and batch systems, apply equally well to mixed mode systems. However,
two major factors make any determination more difficult to make. First, get evidence to show that, in all circumstances, priority is given to
maintaining good interactive response, and that nontrivial tasks really
execute in the background. Second, background tasks matter how
large, inefficient, or demanding) should not be allowed to dominate the
overall use of the time-sharing system. In other words, in mixed mode
operation, get evidence to show that users with poor characteristics are
discriminated against for the sake of maintaining an efficient system
for the remaining users.
A number of other conditions are more obvious and straightforward. For examFle: Measure response time and determine at what point it becomes unacceptable and why. Studies of time-sharing systems have
shown that a user's work rate is closely correlated with the system
response. When the system responds quickly, the user is alert, ready
for the next interaction, and thought processes are uninterrupted. When the system response time is poor, the user loses concentration.
Section 1. General Considerations 37
Generation Procedures Under VM/370 VM/370 can help considerably throughout the system generation process.
Probably VM/370's biggest advantage is the ability to generate the
system under VM/370 without disturbing the normal production activity.
The system programmer (or whoever is responsible for the operating system) can log onto his own virtual machine and go through the
generatien steps at his own pace while the daily work is being
processed. He can use the VM/370 CMS editor to create and update the job streams that are used during system generation. Whenever the system
generaticn Frccess requires, he can use CMS EXEC procedures to pass
these saved jeb streams to the test system. When the system is tested,
it can be placed online, replacing the previous version with minimal interruption to the production activity.
Fer a discussion of the CMS editor and EXEC facilities, refer to the CMS For details about the system generation
procedure for DOS/VS and as/vs under VM/370, refer to these
systell- dependent sections in this publication.
Creating VM/370 Directory Entries To allow a virtual machine to exist in the VM/370 system, the VM/370 system requires a directory entry definition. Each definition is kept
in a directcry entry source file (filetype DIRECt) on a user minidisk.
An installatien lIust use the VM/370 directory program to convert these
source definitions in the V"/370 systell directory file (usually on the
system residence disk) that contains one entry for each virtual machine.
Each directory entry contains a number of directory control
statements that define the virtual machine's configuration and other operational characteristics to VM/370. In general, a virtual machine
ccnfiguration defined in the directory consists of the following: Virtual storage, console, and processor Direct access storage devices unit record devices Other devices
Figure 13 shows the relationship of a directory entry to both the VM/370 system's real devices and the virtual machine's virtual devices.
The installation must keep both the source and system directories
updated. As users submit additions and/or changes, the installation must either create new or update current directory entries. This
updating can be done by using the VM/370 Directory Maintenance program
Product (5748-XE4), the CMS editor, or punched cards. (For more details
about this program product, refer to the GC20-1836.)
To create directory entries for operating systems running in virtual
machines, installations must consider both the general and unique
requirements for specifying directory entries. For general details
atout specifying directory entries, refer to fl!ftftiftg !ftQ For uniqup. details about specifying directory entries
fer operating systems running in a virtual machine, refer to the
fcllowing tepic "Unique Directory Entry Considerations."
36 IBM V5/370 Operating Systems in a Virtual Machine
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