PRIORITY You can assign specific (dispatch) priority values to different
virtual machines to override the assigned or default priority value
for each user in the V6/370 directory. In doing so, the virtual .achine .ith a lover nn value is considered for dispatching before a
virtual machine with a higher nn value. You set user priorities by using the following class A console function: SET PRIORITY userid nn userid is the user's identification
nn is an integer value from 1 to 99. The higher the nn value,
the lower the dispatching priority. V6/370 ASSISTANCE - HARDWARE ASSIST The overhead associated with CP's handling of virtual machines and their
collective I/O resources is extensive and time consuming. To reduce
this overhead, CP is assisted by Systea/370 Frocessor hardware that
duplicates some of the functions provided by CP routines to accelerate CPU processing. This hardware assistance to program function is called VM/370 hardware assist. Some form of V!/370 hardware assist is
available on all V!/370 supported System/370 systems except the models
155, 155II, 165, 165-3, and 4331. V!/370 hardware assist on certain
processors can consist of virtual machine assist; on other processors V!/370 hardware assistance is composed of virtual machine assist and V6/370 Extended Control Program Support (V!/370 ECPS) • V!/370 hardware assist is activated when V!/370 is loaded or by the
use of CP co.mands, and it is deactivated by CP commands. For the command that activates/deactivates the V!/370 hardware assist process,
refer to the SET com.and described in "Section 3. CP Co.mands." The
status of V6/370 hardware assist may be determined by the use of the QUERY command also described in Section 3.
The virtual machine assist facility (V6A) can be ordered via feature number, it is available as an RPQ (Request for Price Quotation), and is
standard on some processors. For a list of V6/370 supported processors
and how they support V!A and ECPS see gnd §yig!. On attached processor syste.s, virtual machine assist
maybe installed on one or both processors. Virtual machine assist
relieves CP of some of the processing overhead caused by the simulated
execution of certain instructions, privileged operation instructions,
and interrupts of virtual machines. On/off system control of virtual machine assist is provided by the A privilege class command: SET SASSIST {ON } OFF [[ PROC] nn] Users of virtual machines, in turn, have discrete control over the
functions of virtual machine assist by means of directory entry options
or by command. For control of this function on a virtual machine level,
refer to the privilege class G command SET ASSIST, described in I2! 32 V!/370 operator's Guide

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