nucleus is relocated and placed beyond the virtual=real machine in real
storage. This option is discussed in more detail in"VM/370 Performance nn";"ft"" " Since the entire address space required by the virtual machine is
locked, these page frames are not available for use by other virtual
machines except when the virtual=real machine isnot on. This
option often increases the paging activity for other virtual machine
users, and in some cases forVM/370. (Paging activity on the system may
increase substantially, since all other virtual machine storage
requirements must be managed with fewer remaining real page frames.)
The virtual=real option may be desirable or mandatory in certain
situations. The virtual=real option is desirable when running a virtual
machine operating system (likeDOS/VS or OS/VS) that performs 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 underVM/370. VM/370 Performance Options VM/370 provides a number of options an installation may use to improve
the performance of virtual machines andVM/370. Several options improve
the performance of installation specified virtual machines; other
options improve the performance of all virtual machines andVM/370. The
options, described in the following discussion are:I • Favored execution I • User priority I • Reserved page frames I • Virtual=real I to.! Affinity I • Virtual machine assist I • Extended Control-Program Support
Specifying a performance option may mean making a performance
trade-off; improving the performance of one virtual machine at the
expense ofVM/370 and other virtual machines. For example, after an
operator specifies favored execution for a virtual machine, that virtual
machine receives more processor time than other virtualmachines= Therefore, before specifying any performance option, identify the
option's performance trade-offs and assess their impact on system
performance.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 machine than would ordinarily be
the case. The options provided are:• The basic favored execution option • The favored execution percentage option
Part 2. Control Program (CP) 93
storage. This option is discussed in more detail in
locked, these page frames are not available for use by other virtual
machines except when the virtual=real machine is
option often increases the paging activity for other virtual machine
users, and in some cases for
increase substantially, since all other virtual machine storage
requirements must be managed with fewer remaining real page frames.)
The virtual=real option may be desirable or mandatory in certain
situations. The virtual=real option is desirable when running a virtual
machine operating system (like
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
the performance of virtual machines and
the performance of installation specified virtual machines; other
options improve the performance of all virtual machines and
options, described in the following discussion are:
Specifying a performance option may mean making a performance
trade-off; improving the performance of one virtual machine at the
expense of
operator specifies favored execution for a virtual machine, that virtual
machine receives more processor time than other virtual
option's performance trade-offs and assess their impact on system
performance.
scheduling algorithms and force the system to devote more of its
processor resources to a given virtual machine than would ordinarily be
the case. The options provided are:
Part 2. Control Program (CP) 93