8.111 NUMCPU (Display or set number of emulated CPUs)

8.111.1 Function

The NUMCPU commands displays or sets the number of emulated processor engines which will be con-
figured online at startup time. The combination of NUMCPU and MAXCPU controls the behaviour of how
many CPU engines will be configured online upon startup and how many can be configured online later.

NUMCPU cannot exceed the value of MAXCPU. If NUMCPU is less than MAXCPU then the remaining
engines can be configured online later. The default NUMCPU value is 1. All processors are CP engines
unless otherwise specified by the ENGINES system parameter.

Multiprocessor emulation works best if your host system actually has more than one physical CPU, but
you can still emulate multiple CPUs nevertheless even on a uniprocessor system (and you might even
achieve a small performance benefit when you do).

There is little point, however, in specifying NUMCPU greater than 1 unless your guest operating system
(running under Hercules) is actually able to support multiple CPUs. If you do not actually need
multiprocessor emulation, then setting MAX_CPU_ENGINES to 1 at compile time might even produce a
slight performance advantage too.

Given without an argument the NUMCPU command displays the current number of emulated CPUs.

For detailed explanations on the interrelationship between NUMCPU, MAXCPU and ENGINES please
see “

8.111.2 Syntax

Descriptive

[nn]

Diagram

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nn

8.111.3 Parameter

nn

The number of emulated CPUs. NUMCPU must be less than or equal MAXCPU. If
NUMCPU is larger than MAXCPU then an error message is issued, if it is less than
MAXCPU then the remaining engines can be configured online later.

8.111.4 Examples

Example 1:

Display the current number of emulated CPUs.

HHC00013I Herc command: 'numcpu'

HHC02203I numcpu : 2

Figure 211: NUMCPU command (display current number of emulated CPUs)

Example 2:

Set the number of emulated CPUs to 4 (increase from 2 currently).

HHC00013I Herc command: 'numcpu 4'

HHC00100I Thread id 0000080C, prio 0, name 'Processor CP02' started

HHC00811I Processor CP02: architecture mode 'S/370'

HHC00100I Thread id 00000CB4, prio 0, name 'Processor CP03' started

HHC00811I Processor CP03: architecture mode 'S/370'

HHC02204I numcpu set to 4

Figure 212: NUMCPU command (increase emulated CPUs)

Example 3:

Set the number of emulated CPUs to (reduce from 4 currently).

HHC00013I Herc command: 'numcpu 2'

HHC00101I Thread id 0000080C, prio 0, name 'Processor CP02' ended

HHC00101I Thread id 00000CB4, prio 0, name 'Processor CP03' ended

HHC02204I numcpu set to 2

Figure 213: NUMCPU command (reduce emulated CPUs)