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
Performance Guidelines
Calculate the amount of available real
amount of storage required by CP from
is:
storage (ARS) by subtracting the
the real machine size. Formula 1
r r" I IRM - 256KI I ARS = RM - II + T + 12K + 4KI---------1 I I I 64K II L L .J.J RM is the real machine size.
I is the amount of storage needed to IPL CP. Refer to the load
map produced when the CP nucleus is generated. The amount of
storage needed to IPL CP is all of storage up to, and
including, the module DMKSAV. T is the amount of storage allocated for the CP internal trace
table. CP allocates 4K of storage for each 256K of real
storage for the CP internal trace table:
r , I RM I 4K 1----1 f256KI L .J
If the calculation RM/256K results in a fraction, the result
should be rounded upward to the next higher integer.
12K is the amount of fixed free storage allocated for the first
256K of real storage.
r , IRM - 256KI 4KI---------I I 641{ , L .J
is the amount of fixed free storage allocated for real storage
beyond the first 256K (if there is no virtual=real area). If
the calculation enclosed in brackets results in a negative
value, replace it with zero. If the same calculation results
in a fractional number, disregard the fraction.
The result obtained from Formula 1 is the amount of available real
storage (ARS) for a particular real machine size. This result is needed
to calculate the maximum size of a virtual=real area in Formula 2.
12 IBM VM/37Q Planning and System Generation Guide
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