Note: In attached processor mode, no shared pages are locked. If the
system operator attempts to lock a shared page or an address range
containing one or more shared pages, he will receive the message DMKCPV165I PAGE (hexloc) NOT LOCKED, SHARED PAGE
for each of the shared pages within the range. RESERVED PAGE FRAMES OPTION A more flexible approach than locked pages is the reserved page frames option. This option provides a specified virtual machine with an
essentially private set of real page frames, the number of frames being designated by the system operator, when he issues the CP SET RESERVE command line: Pages will not be locked into these frames. They can be
paged out, but only for other active pages of the same virtual machine. When a temporarily inactive virtual machine having this option is
reactivated, these page frames are immediately available. If the
program code or data required to satisfy the request was in real storage
at the time the virtual machine became inactive, no paging activity is
required for the virtual machine to respond.
This option is usually more efficient than locked pages in that the
pages that remain in real storage are those pages with the greatest
aaount of activity at that moment, as determined automatically by the system. Although multiple virtual machines may use the LOCK option,
only one virtual machine at a time may have the reserved page frames option active. Assignment of this option is discussed further in
npreferred Virtual Machines.
n The reserved page frames option provides performance that is
generally consistent from run to run with regard to paging activity.
This can be especially valuable for production-oriented virtual machines
with critical schedules, or those running teleprocessing applications
where response times must be kept as short as possible. YIRTU1L=RE1L OPTION The VM/310 virtual=real option eliminates CP paging for the selected
virtual aachine. 111 pages of virtual machine storage, except page
zero, are locked in the real storage locations they would use on a real
coaputer. CP controls real page zero, but the remainder of the CP
nucleus is relocated and placed beyond the virtual=real machine in real
storage. This option is discussed in more detail in "Preferred Virtual Machines.
n Since the entire address space required by the virtual machine is
locked, these page frames are not available for use by other virtual
aachines except when the virtual=real aachine is not logged on. This
option often increases the paging activity for other virtual machine users, and in some cases for VK/310. (Paging activity on the system .ay
increase substantially, since all other virtual machine storage
requirements aust be aanaged with fewer remaining real page fraaes.)
CP Introduction 1-29

The virtual=real option may be desirable or mandatory in certain
situations. The virtual=real option is desirable when running a virtual machine operating systea (like DOS/VS or OS/VS) that perforas paging of
its own because the possibility of double paging is eliminated.. The
option must be used to allow programs that execute self-modifying channel programs or have a certain degree of hardware timing
dependencies to run under VM/310. Preferred Virtual Machine Options Vft/310 provides seven functions that create a special virtual machine environment:
1. Favored execution
2. Priority
3. Reserved page frames 4. Virtual=real option !ffi!!it! 6. Virtual machine assist
1. Extended Control-Program Support
The first five functions are designed to improve the performance of a
selected virtual aachine; the last two functions improve the performance of VM/310. Although each of the first five functions could be applied
to a different virtual machine, usually they are applied to only one if optimum performance is required for that one specific virtual machine. The sixth and seventh functions can be applied to as many virtual machines as desired. FAVORED EXECUTION The favored execution options allow an installation to modify the normal scheduling algorithms and force the system to devote more of its
processor resources to a given virtual aachine than would ordinarily be
the case. The options provided are:
1. The basic favored execution option.
2. The favored execution percentage option.
The basic favored execution option means that the virtual machine so
designated is not to be dropped from the active (in queue) subset by the
scheduler, unless it becomes nonexecutable. When the virtual machine is
executable, it is to be placed in the dispatchable list at its normal priority position. However, any active virtual machine represents
either an explicit or iaplicit coamitment of main storage. In explicit
storage com.itment can be specified by either the virtual=real option or
the reserved page frames option. In implicit commitaent exists if
neither of these options is specified, and the scheduler recoaputes the
virtual machine's prOjected work-set at what it vould noraally have been
at queue-drop time. Multiple virtual machines can have the basic
favored execution option set. However, if their combined main storage
requirements exceed the system's capacity, performance can suffer
because of thrashing.
If the favored task is highly compute bound and must coapete for the
processor with aany other tasks of the same type, an installation can
define the processor allocation to be aade. In this case, the favored
execution percentage option can be selected for one virtual aachine. 1-30 IBft VM/310 System Logic and Problem Determination--Volume 1