Performance Guidelines
Determine the maximum size virtual=real area for a real machine with
1792K of real storage. The V"/370 system requires 244K to IPt. r r, r " 1 11192KI 11192K - 256KII ARS = 1192K - 1244K + 4KI-----I + 12K + 4KI------------I' I I 256KI ,64K II L L.I L .1.1 ARS = 1192K - [244K + 4K[1] + 12K + 4K[24]] ARS = 1192K - [244K + 28K + 12K + 96K] A RS = 179 2K -[3 8 OK ] ARS = 1412K r r " I 11192K - 256K - 1412KI 1 VRS = 1192K - 1244K + 28K + 12K + 4KI--------------------I + 16K I , I 64K I I L L .1.1 r r, , I 11241 I VRS = 1192K - 1284K + 4KI---I + 16K, I I 64, I L L.I .I VRS = 1792K - [308K] VRS = 1484K Note that the fraction (124/64) resulting from the R" - 256K - ARS 64K calculation in Formula 2 is rounded to the next higher integer, two.
16 VM/370 Planning and System Generation Guide
Performance Guidelines
Determine the maximum size virtual=real area for a real machine with
256K of real storage. The VK/370 system requires 244K to IPt. r r, r " I I 256K I 1256K-256K I I ARS = 256K - 1244K + 4KI----I + 12K + 4KI---------1 I , 1256KI I 64K I I L L L ARS = 256K -[244K + 4K[ 1 ] + 12K + 4K[ 0]] ARS = 256K - [26 OK] ARS = -4K Since ARS is a negative number, CP cannot IPL and the following error
message informs the user of this condition: DKKCPI955W INSUFFICIENT STORAGE FOR VM/370 Virtual Machine Assist Virtual machine assist is a combination of a processor feature and VK/310 programming. It improves the performance of VM/370. Virtual storage operating systems that run in problem state under the control of VM/310 use many privileged instructions and SVCs that cause interrupts
which VK/370 must handle. When virtual machine assist is used, many of
these interrupts are intercepted and handled by the processor; and,
consequently, VM/370 performance is improved. The manner in which
virtual machine assist and ECPS are supported by the various VM/370 processors is detailed under "Using the Performance Options."
Certain interrupts must be handled by VM/370. Consequently, virtual
machine assist is not available if it: Has an instruction address stop set Traces SVC and program interrupts Since an address stop is recognized by an SVC interrupt, VM/370 must
handle SVC interrupts while address stops are set. Whenever you issue
the ADSTOP command, VM/370 turns off the SVC handling portion of the
assist feature for your virtual machine. The assist feature is turned on
again after the instruction is encountered and the address stop removed. Whenever a virtual machine issues a TRACE command with the SVC, PRIV, BRANCH, INSTRUCT, or ALL operands, the virtual machine assist feature is
turned off for that virtual machine. The assist feature is turned on
again when the tracing is completed.
Part 1. Planning for System Generation 17
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