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
Performance Guidelines
If virtual machine assist is available on a processor, the operator
can turn the function off, and on again, for the entire VM/310 system.
Also, if the function is available to VM/310, each virtual machine
operator can turn the function off, and on again, for his own virtual
machine. When you create your VM/370 directory, you can set off the SVC-handling portion of the virtual machine assist function for various
virtual machines by specifying SVCOFF on the OPTION control statement. VM/370 EXTENDED CONTROL-PROGRAM SUPPORT V"/370 Extended control-Program Support is a
that provides support over and above that
machine assist feature described previously, VM/370's real supervisor state time needed to VM/370 Extended Control-Program Support
functions. virtual machine assist CP assist Virtual interval timer assist
hardware assist function
provided by the virtual
and consequently reduces
support virtual machines.
provides the following Whenever VM/370 is loaded on one of the supported processors, all three
hardware assist functions plus virtual machine assist are activated
unless turned off by the system operator.
Expanded virtual machine assist includes a more comprehensive
emulation of the SSM, LPSW, STNSK, and STOSM privileged instructions.
Additional privileged instructions are also emulated. CP assist provides a hardware assist for the high-use portions of the
following CP functions: Virtual machine I/O Storage management Page management SVC handler Privileged instruction handler Dispatcher
If (1) CP assist is turned off, (2) hardware assist does not support the
specific service required, or (3) an error condition occurs, the
appropriate CP software routine is used. Virtual interval timer assist provides for hardware updating of the
location 80 interval timer for each virtual machine that has the virtual
timer assist function turned on. This timer assist provides a more
accurate and repeatable interval timer value for virtual machines than
was previously possible through CP software.
Both virtual machine assist and expanded virtual machine assist are
automatically turned off if the user invokes certain TRACE functions.
In addition, virtual interval timer assist is turned off if external
interrupts are traced. When the tracing function is terminated, CP automatically reactivates these V"/370 hardware assist functions.
For more details on VK/370 Extended control-Program Support, refer to
the Qyide. 1A VM/370 Planning and System Generation Guide
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