The virtual ASP system (VM1 and VM2) shown in Figure 11 may be used
in one of two ways: (1) to install and test a new ASF release, or (2)
fer ASP system testing in a virtual environment concurrent with normal
pr.oduction. The virtual ASP system eliminates the need to dedicate the
real ASP system for new system testing.
The V8/370 must contain a
in the form:
directory entry for each of
statement defining a virtual
the virtual ASP processors
channel-to-channel adapter SPECIAL 280 CTCA
where: 280 is the address of the channel-to-channel adapter as generated
in the operating system. When both virtual ASP machines are logged onto VM/370, the CF COUPLE command must be issued by one of the virtual machine operators:
couple 280 to vm2 380 where: 280 is the address of VM1's virtual channel-to-channel adapter, VM2 is the userid of the second virtual machine. and 380 is the
address of VM2's virtual channel-to-channel adapter. After the
channels are coupled, the operator of each virtual machine can
then load his operating system and start running ASP. The second way, as shown in Figure 12. has an additional virtual machine (VM3), with a real channel-to-channel adapter to a real
System/360 cr System/370, running as either the main or support
processor in a production ASP system.
System/370
r I I VM3 OS/ASP Main I Processor I L ____________ VM/370 L- r
Real eTC
, I I 1 I as/ASP I Support I Processor I I System/370 Model 145
Figure 12. One Real and One Virtual ASP Machine
32 IBM VM/370 Operating Systems bn a Virtual

Define the real channel-to-channel adapter in the VM/370 system
generation procedure by using the RDEVICE macro instruction with a
device type of CTCA (DEVTYPE=CTCA). The virtual machine (VM3) must have
this device assigned to it before the IPL. Make this assignment by using
the DEDICATE statement in the virtual machine's VM/370 directory entry,
such as:
DEDICATE 280 380 where: 280 is the of the channel-to-channel adapter as generated
in the os system, and 380 is the address of the real
channel-to-channel adapter as specified in the VE/370 system procedure.
If no DEDICATE statement for the channel-to-channel adapter appears
in the virtual machine's directory entry, a resource operator with
privilege class B must attach the real channel-to-channel adapter to the
virtual machine.
Note: For further information on the virtual channel-to-channel adapter,
refer to the description of the COUPLE, DEFINE, and DETACH commands in
the ]ser§. Performance Guidelines When run in a virtual machine, the performance characteristics of an
operating system are difficult to predict. This unpredictability is a
rEsult of the complex interaction of many factors that affect
performance. These factors can be broadly classified into three groups: • Configuration factors • Workload factors • VM/370 performance factors
Performance of any virtual machine may be improved by the choice of
hardware configuration, operating system workload, and VM/370 performance options. While a specific virtual machine's performance may
not equal that of the same operating system running stand-alone on the
same System/370, in some situations the total throughput obtained in the
virtual machine environment can be equal to, or better than, that
obtained on a real machine.
These hardware configuration factors influence the performance of an
operating system in a virtual machine: • The System/370 model used. • The amount of real storage available. • The speed, capacity, and number of paging devices. • The degree of channel and control unit contention, as well as arm
contention, affecting each paging device. • Whether virtual machine assist or VM/370 extended control-program is installed on the hardware and enabled. • Interference between system paging devices and devices for processing
a user's I/O requests.
Section 1. General Considerations 33