QE!!Qn§: After measuring the performance of both VM/370 and the virtual machines it supports, the system analyst and the
general user can each use certain VM/370 performance options. These oftions allow them to create a special performance environment for one
cr more virtual machines. The options allow: • The system analyst to redistribute system resources either to balance
inequities or to favor one virtual machine over another. • The general user to improve the performance for his virtual machine.
The VM/370 system operator, on behalf of the system analyst, can give
certain oftions to a specific virtual machine to improve its performance
over other virtual machines. A general user has certain performance
options that give limited control over his virtual machine. The options
available to the system operator and the general user are: Locked pages option
Reserved page frames
Priority
Favored execution option Virtual machine assist VM/370 extended control-program support Virtual=real option
1
In the following list, the first option and either of the next two oftions can be applied to only one virtual machine at a time. • Favored execution with guaranteed percentage • Reserved page frames • Virtual=real option
1
The following options can be applied to as many virtual machines
as desired: • Basic favored execution (without guaranteed percentage) • priority • Virtual machine assist • VM/370 extended control-program support (HepS: • Locked pages
For basic information about these options, refer to the For details about specifying the options for the
system operator, refer to Guide. For details about
specifying the options for the general user, refer to f££ The System Extensions program Product (S748-XE1) provides several performance-related additions to the system control program. For certain environments, these additions: • Improve throughput • Provide better terminal response
1This option cannot be specified in a command. To obtain it. a qenpral user requests the VM/370 system programmer to specify it on control statement (VIRT=REAL option) for the user's virtual machine
directory entry_ 36 :BM VM/370 operating Systems in a Virtual Machine

• 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