Performance Guidelines General Information
The performance characteristics of an operating system, when it is run
in a virtual machine environment, are difficult to predict. This
unpredictability is a result of several factors:• The System/370 model used. • The total number of virtual machines executing. • The type of work being done by each virtual machine. • The speed, capacity, and number of the paging devices. • The amount of real storage available. • The degree of channel and control unit contention, as well as arm
contention, affecting the paging device.• The type and number of VM/370 performance options in use by one or
more virtual machines.I • The degree of MSS 3330 volume use.
Performance of any virtual machinemay be improved up
by the choice of hardware, operating system, andVM/370 topics discussed in this section address:
to some limit
options. The
1. The performance options available inVM/370 to improve the
performance of a particular virtual machine.
2. The system options and operational characteristics of operating
systems running in virtual machines that will affect their
execution in the virtual machine environment.
The performance of a specific virtual machine may never equal that of
the same operating system running standalone on the sameSystem/370, but
the total throughput obtained in the virtual machine environment may
equal or better that obtained on a real machine.
When executing in a virtual machine, any function that cannot be
performed wholly by the hardware causes some degree of degradation in
the virtual machine's performance. As the control program for the real
machine,CP initially processes all real interrupts. A virtual machine
operating system's instructions are always executed in state.
Any privileged instruction issued by the virtual machine causes a real
privileged instruction exception interruption.1he amount of work to be
done byCP to analyze and handle a virtual machine-initiated interrupt
depends upon the type and complexity of the interrupt.
The simulation effort required of CP may be trivial, as for a
supervisor call(SVC) interrupt (which is generally reflected back to
the virtual machine), or may be more complex, as in the case of aStart I/O (SIO) interrupt, which initiates extensive CP processing.
88IBM VM/370 System Programmer's Guide
The performance characteristics of an operating system, when it is run
in a virtual machine environment, are difficult to predict. This
unpredictability is a result of several factors:
contention, affecting the paging device.
more virtual machines.
Performance of any virtual machine
by the choice of hardware, operating system, and
to some limit
options. The
1. The performance options available in
performance of a particular virtual machine.
2. The system options and operational characteristics of operating
systems running in virtual machines that will affect their
execution in the virtual machine environment.
The performance of a specific virtual machine may never equal that of
the same operating system running standalone on the same
the total throughput obtained in the virtual machine environment may
equal or better that obtained on a real machine.
When executing in a virtual machine, any function that cannot be
performed wholly by the hardware causes some degree of degradation in
the virtual machine's performance. As the control program for the real
machine,
operating system's instructions are always executed in
Any privileged instruction issued by the virtual machine causes a real
privileged instruction exception interruption.
done by
depends upon the type and complexity of the interrupt.
The simulation effort required of CP may be trivial, as for a
supervisor call
the virtual machine), or may be more complex, as in the case of a
88