This option specifies that the selected virtual machine, in addition to remaining in queue, is guaranteed a specified minimum percentage of the
total processor time if it can use it. The favored execution option can
only be invoked by a system operator with command privilege class A. The format of the command is as follows: r , SET FAVORED userid Inn I L userid identifies the virtual machine to receive favored execution
status.
nn is any value from 1 through 99 and specifies the percentage
of the in-aueue time slice that is guaranteed to this virtual machine. OFF specifies that the virtual machine is to be removed from favored execution status.
The percentage option of the SET FAVORED command is administered as
follows:
1. The in-queue time slice is multiplied by the specified percentage
to arrive at the virtual machine's guaranteed processor time. 2. The favored virtual machine, when it is executable, is always
placed at the top of the dispatchable list until it has obtained
its guaranteed processor time. 3. If the virtual machine obtains its guaranteed processor time before
the end of its in-queue time slice, it is placed in the
dispatchable list according to its calculated dispatching priority.
4. In either case (2 or 3), at the end of the in-queue time slice the
guarantee is recomputed as in step 1 and the process is repeated. Whether or not a percentage is specified, a virtual aachine with the favored execution option active is kept in the dispatching queues except
under the following conditions: • Entering CP console function mode • Loading a disabled PSW • Loading an enabled PSW with no active I/O in process • Logging on or off When the virtual machine becomes executable again, it is put back on the
executable list in Q1. If dropped from Q1, the virtual machine is
placed directly in Q2 and remains there even though it may exhaust its
allotted amount of processor usage. Virtual machines with this option
are thus considered for dispatching more frequently than other virtual machines. Note, however, that these options can impact the response time of
interactive users and that only one favored percentage user is allowed
at any given time. CP Introduction 1-31

PRIORITY The VM/370 operator can assign specific priority values to different
virtual machines. In so doing, the virtual machine with a higher
priority is considered for dispatching before a virtual machine with a
lower priority. User priorities are set by the following class 1 command:
SET PRIORITY userid nn
where userid is the user's identification and nn is an integer value from 1 to 99. The value of nn affects the user's dispatching priority
in relation to other users in the system. The priority value (nn) is
one of the factors considered in VM/370's dispatching algorithm. Generally, the lower the value of nn, the aore favorable the user's
position in relation to other users in VM/370's dispatch queues. RESERVED PAGE FRAMES VM/370 uses chained lists of available and pageable pages. Pages for
users are assigned from the available list, which is replenished from the pageable list.
Pages that are temporarily locked in real storage are not available
or pageable. The reserved page function gives a particular virtual machine an essentially "private" set of pages. The pages are not
locked; they can be swapped, but only for the specified virtual machine. Paging proceeds using demand paging with a "reference bit" algorithm to
select the best page for swapping. The number of reserved page frames for the virtual machine is specified as a maximum. The page selection algorithm selects an available page frame for a reserved user and marks that page frame "reserved" if the maximum specified for the user has not
been reached. If an available reserved page frame is encountered for the
reserved user selection, it is used whether or not the maximum has been
reached.
The maximum number of reserved page frames is specified by a class A co.mand of the following format:
SET RESERVE userid xxx where xxx is the maximum number required. If the page selection algorithm cannot locate an available page for other users because they
are all reserved, the algorithm forces the use of reserved pages. This
function can be specified in only one virtual machine at anyone time. !Qte: xxx should never approach the total available pages, since CP overhead is substantially increased in this situation, and excessive paging activity is likely to occur in other virtual machines. VIRTUAL=REAL For this option, the '8/370 nucleus .ust be reorganized to provide an
area in real storage large enough to contain the entire virtual=real machine. In the virtual machine, each page from page 1 to the end is in
its true real storage location; only its page zero is relocated. The
virtual machine is still run in dynamic address translation mode, but
1-32 IBM VM/370 System Logic and Problem Determination--Volume 1