When virtual machine activity is initiated ?n an infrequent or basis, such as from a remote terminal a teleprocessing system, some (or all) of its virtual storage may be paged out before the
virtual machine begins processing. The paging activity required for the
virtual machine to respond to the teleprocessing request may increase
the time required to respond to the request. Use the locked pages or reserved page frames options to improve
performance.
If the Frogram must be run in the dynamic paging area, then locking
specific pages of the virtual machine into real storage may ease the
problem. However, besides page zero and the page containing the TF interruption handler, it is not always easy or possible to identify
which specific pages are always required.
A more flexible approach than locked pages is the reserved page
frames option. When a temporarily inactive virtual machine having this
cption is reactivated, these page frames are immediately available. If
the program code or data required to satisfy the request was in real
storage at the time the virtual machine became inactive, no paging
activity is required for the virtual machine to respond.
For details about the locked pages and reserved page frames options,
refer to the 2Y§1gm THE ASP VIRTUAL MACHINE When using the OS asymmetric multiprocessing system
installation find virtual machines useful in two ways. (ASP) , an
The first way, as shown in Figure 11, has a
can be run by two virtual machines eVM1 and
channel-to-channel adapter (CTCA).
virtual ASF system that VM2) using a virtual VM1 OS/ASP Main Processor I System/370 -----. VM2 I , r_-------, I I I I as/ASP Support Processor I I I I I I L- _____________ J I I Virtual eTC A
L ______________________ I I I , VM/370 I __________________________________________ J
Figure 11. Two ASP Virtual Machines Section 1. General Considerations 31

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