Real Storage Addresses
r--------------------------------------------------------512i----- VIRTUAL STORAGE POOL for other users RELOCATED CP NUCLEUS RELOCATED PAGE ZERO for the DOS aachine (locked in real storage)
156K DOS VIRTUAL=REAL KACHINE CP PAGE 0 Figure 2. DOS 160K Virtua1=Rea1 Storage Assignaents LOCKED PAGES OPTION 260K 164K 160K 4K
If sufficient page fraaes are available for other users, you can choose
to lock (fix) one or aore specific pages of a virtual aachine or the
pageab1e CP nucleus in real storage. This perforaance option differs
from the other options in that the LOCK command can apply to several
virtual machines. It is also possible to the reserved page fraaes
option apply to one user's virtual machine, and then have the lock
option apply to another user's virtual aachine. A locked page is
effective froa the tiae you invoke the lock option until the user logs
off the systea, or until you issue the UNLOCK co.mand. If the page or
pages that are locked have a high frequency of reference or change
activity, the lock option, like the reserved option, can cause an improvement in the user's virtual aachine performance or overall system performance because of the reduction in paging activity. Notes: ':---If a naaed systea currently has the locked pages option in effect,
reloading of the saae naaed system, loading of another systea, or a systea reset does not affect the locked· pages option of a
virtual The loading of named systems named systeas without using the UNLOCK coa.and beforehand results in pages
being made u,navailable for use if the first naaed syste. has locked pages in effect.
2. In an attached processor systea shared pages cannot be locked.
3. You should always prefer the reserved page frames option to the
locked pages option, if it is not already in use. The LOCK command locks specific pages into real storage regardless of activity, while
the reserved page frames option keeps all the currently aost active
pages in real storage.
section 2. Initiating V8/370 Operation 31

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