V8/370 Extended Control-Program support is an expansion of the function
provided by virtual machine assist and consists of three major parts: • Expanded virtual machine assist • CP assist • Virtual interval timer assist
Expanded virtual machine assist is an expansion of function provided by virtual aachine assist in that, via hardware. CP is relieved of
processing soae conditions of CP simulated instruction execution that
were not covered by the virtual machine assist process. Expanded
virtual machine assist also assists CP in the processing of other
instructions and privileged operations not emulated by virtual aachine
assist.
Expanded virtual machine assist is activated for all virtual aachines
when V8/370 is loaded. It is also activated when both class A commands
are invoked as shown: SET SASSIST ON --and-- SET CP1SSIST ON Expanded virtual machine assist is deactivated when either SET SlSSIST OFF or SET CPASSIST OFF is invoked.
The CP assist portion of the V5/310 Extended Control-Program support
duplicates via hardware the function provided by various high-usage
significant overhead portions of CP routines. CP assist is activated
upon system initialization or by invoking the privilege class 1 coamand: SET CPASSIST ON When the OFF operand of CPASSIST is invoked
l CP assist
(as well as expanded virtual machine assist portion
previously active).
is deactivated
of ECPS, if
The third function provided by V8/370 ECPS is virtual interval
assist. This hardware assist provides virtual aachines with a
accurate method of updating the virtual machine's interval
tiaer more tiaer
by the
of .this
.class G
on this,
(location X'SO'). Overall system control of this function is
class 1 coamands SET SASSIST ON and SET SASSIST OFF. Control
facility on the individual virtual machine level is by the
coamand SET ASSIST T!R and SET ASSIST NOT8R. For aore details
refer to the 18/370 Coamgng fo£ To summarize the use of the SET relationship to virtual aachine
Control-Program Support, see Figure 3. CPASSIST and
assist and SET SlSSIST in V8/370 Extended
Section 2. Initiating V8/370 Operation 33

I 1 '-I I I I I SET I SET I SET I SET I ISASSIST ON ISASSIST ON ISASSIST OFF I SASSIST OFF I V!/370 I SET I SET I SET I SET IHardware Assist ICPASSIST OFFICPASSIST ON ICP1SSIST ON ICP1SSIST OFF I I I I I iiirtual Machine v • V I I A I A I , I Assist I I I I • I I I I .. IVirtual Intervall X I X I I I I Timer Assist I I I I I • I I I I I IExtended virtual I I X I I I I !achine Assist I I I I I • I I I I I ICP Assist I I X I I I , f f f • I I , , • I .. ILegend: X = function activated I I Figure 3. Command Control of V!/370 Hardware Assist A virtual machine running in certain virtual machine modes or running
certain operations cannot use certain facilities provided by Vft/370 hardware assist. When these modes or operations are encountered, the
action taken is dependent upon the processor facilities of either
virtual machine assist or V!/370 Extended Control-program Support.
For all V!/310 supported processors that have V!/370 hardware assist
active when the CP ADSTOP or certain CP TRACE command functions are
encountered, the virtual machine assist is deactivated during the
interval of their use.
For System/310 Models 135-3, 138, 145-3, and 148, the use of the DOS emulator or PER (prograa Event Recording) curtails some of the function
provided by VM/370 Extended Control-Program SUPFort. For aore details
on VM/310 hardware assist, see the §Yide. AFFINITY In Attached Processor systems a virtual aachine aay be designated to
execute only on one specified processor. This may be advantageous for
performance or functional requirements. Performance gains might be
realized with affinity because of the nature of the workload or the
availability of performance assists on one processor. Functional
requirements could be the existence of required operation codes on one
processor. In either case, CP code executed on behalf of the virtual machine aay execute on either processor. 34 'M/370 Operator;s Guide