Performance Guidelines
This problem may be counteracted by using the FREE operand in the SYSCOR macro instruction in the system control (DMKSYS) file at system
generation. The SYSCOR macro is described in "Part 2. Defining Your V8/370 System." The examples used in the following discussions assume
that you are allowing V8/370 to determine the number of free storage
pages to allocate.
To use the virtual=real option effectively on a multiport
teleprocessing system with no CCW translation (SET NOTRANS ON), lines
must be dedicated to that system via the ATTACH command or by V8/370 directory assignment. Conversely, on a multiport teleprocessing
virtual=real operation, virtual 2701/2702/2703 lines, (that is, lines
assigned and used by CP's DEFINE and DIAL operate with CCW translation. If you issue the DIAL command while SET NOTRANS ON is in
effect, CCW translation is done for I/O involving that line.
Note that you cannot execute programs with dynamic or self-modifying
channel programs in a virtual=real area if you also use the DIAL
command. Also, you cannot load (via IPL) a shared into a virtqal machine running in the virtual=real area. For a virtual=real machine,
you must issue the IPL command with either a device address or the name
of a non shared system.
To generate CP so that it properly supports a virtual=real area, do
the following: • Specify the VIRT=REAL option in the
virtual machines in your installation
virtual=real area. VM/370 directory for all the
that you plan to run in the • Reserve enough DASD space for the CP nucleus. A CP nucleus that
supports a virtual=real area is larger than one that does not. • Make sure the virtual machine you are using to generate CP has
sufficient virtual storage. • Specify the amount of storage you want reserved for a virtual=real
area.
"Part 2. Defining Your V8/370 System" describes the Directory
program, including information about the VIRT=REAL operand of the OPTION control statement. RESERVING DASD SPACE FOR A CP NUCLEUS WITH A VIRTUAL=REAL AREA
A CP nucleus with the virtual=real option requires more DASD space for
system residence than a CP nucleus without the option. Use the
following formulas to calculate the number of cylinders needed for
system residence (disregard any remainders):
Number of 2314/2319 cylinders = (128+(VRSIZE/4»/32 Number of 3330/3333 cylinders = (171+(VRSIZE/4»/57 Number of 2305/3340 cylinders = (144+(VRSIZE/4»)/24 Number of 3350 cylinders = (240+(VRSIZE/4»/120 where VRSIZE is the size of the virtual=real storage area (in K bytes).
K represents 1024 bytes. This size must be at least 32K bytes. 10 IBM V8/370 Planning and System Generation Guide

Performance Guidelines
The number of cylinders you calculate here is the number you reserve
on your system residence device using the FORMAT program DMKFMT. You need this information to code the SYSRES macro of your CP system control (DMKSYS) file correctly.
If you do not reserve enough DASD space for your CP nucleus, the
nucleus overlays other cylinders when it is written on the system
residence volume and may itself be overlaid by other disk writes. VIRTUAL STORAGE REQUIREMENTS When you are generating VM/370 you have three constraints on the maximum
virtual=real size you can specify: real storage, virtual storage, and
the size of your nucleus.
Before you load the CP nucleus, be sure the virtual machine you are
using has enough virtual storage to contain: • CMS (320K) • CP nucleus size (including the virtual=real area)
If your virtual machine does not have enough virtual storage, redefine
storage and 1PL again before continuing. SPECIFYING THE AMOUNT OF VIRTUAL=REAL SPACE If you are generating your VK/370 system to include a virtual=real
machine, in step 16 of the system generation procedure you respond "yes" to the system message: VIRTUAL=REAL OPTION REQUIRED (YES, NO) : You are then prompted to enter the size of the virtual=real machine
size: STORAGE SIZE OF VIRT=REAL (MINIMUM IS 32K): you would not want to specify the largest virtual=real machine
possible, since that would leave few-page frames available for other
virtual machines.
At IPL time, the virtual=real area is locked in storage immediately
following CP page O. The system operator can issue the UNLOCK command
with the VIRT=REAL option to free the virtual=real area for additional
dynamic paging space for other virtual machines. The area cannot be
relocked; it remains unlocked until another system IPL. Calculate the maximum amount of virtual=real storage available on
your real CPU as follows: • Use Formula 1 to calculate the amount of real storage above the
minimum required by CP at IPL time. If available real storage (ARS) is negative or zero, CP will not IPL. • Use Formula 2 to calculate the
any real machine size. If VRS area is not supported.
maximum virtual=real size (VRS) for
is negative or zero, a virtual=real Part 1. Planning for System Generation 11