When running VS1 in a V=R machine, a user can avoid data transfer
operations into real page zero by doing one of the following: • If the VS1 nucleus already exists, replace the existing ORDFR statement with the following linkage editor control statement in the VS1 linkage editor deck: ORDER IEAAIHOO,IEAIOSOO(P) Use all INSERT control statements that were produced during the
original VS 1 system genera tion process. • Generate a new VS1 nucleus prior to stage II execution and perform lOS alignment by modifying the ORDER control statement in the VS1 stage II job stream. VM/VS HANDSHAKING FOR VS1 VM/VS handshaking is a communication path between the control program
(CP) component of VM/310 and VS1 Release 4 (and subsequent releases)
running as a virtual machine under VM/310. To improve their operation with V8/310, systems generated to use VM/VS handshaking can run both in a real machine and in a virtual
machine. In a virtual machine, systems that have VH/VS handshaking can
more realistically simulate the operation of their real machine. • VH/VS handshaking consists of:
Closing CP spool files when job output
allows VM/310 to immediately process
operator intervention.
is complete.
these output
This fu nction
files without • Processing pseudo page faults. When the pseudo page fault handling
portion cf handshaking is active, one task can be dispatched while
ancther is waiting for a page to be brought into real storage. • Providing a nonpaging mode to eliminate duplicate paging. • Providing a way to avoid a PCI (programmed-controlled interruption)
in a BTAM autopoll CCW loop. • Providing miscellaneous enhancements when running under V8/310. Althcugh handshaking is a system generation feature for VS1, it is
active only when VS1 is run under the control of V8/310; it is disabled
when that same VS1 operating system is run on a real machine. The V8/VS bandshaking feature is active when: • VS1 is generated with the VM/310 option. • The virtual machine storage space is at least 1 megabyte.
Note: If mode is used, refer to the subtopic "VS1 Nonpaging Mcde" described later in this discussion. 110 IBM 370 operating systems in a Virtual Machine

When loading a Vs1 virtual machine that has the handshaking feature,
the VS1 initialization routines determine whether the handshaking
feature is available. VS1 checks for V8/370 by issuing an STIDP (store processor ID) instruction. When STIDP returns the version code X'FF', VS1 is running under V8/370. On receiving version code X'FF', VS1 issues a DIAGNOSE code X'OO' instruction tc store the V8/370 extended-identification code. If V8/370 returns a code to VS1, VM/370 supports handshaking; otherwise, VM/370 does not support handshaking.
The psuedo page fault portion of handshaking may be turned on and off
with the CP SET PAGEX command. When using the CP IPL command again, PAGEX is turned off.
A page fault is a program interruption that occurs when a page marked
"not in storage" is referred to by an instruction within an active page. V8/370 places the virtual machine operating system referring to the page
in a wait state while the page is brought into real storage. Without handshaking, V8/370 places the entire VS1 virtual machine in page wait
until the needed page is available.
However, with handshaking, a multiprogramming (or multitasking) VS1 virtual machine can dispatch one task while waiting for a page request
tc be answered for another task. V8/370 passes a pseudo page fault
(program interruption X'14') to VS1. When VS1 recognizes the pseudo
page fault, it places only the task waiting for the page-in page wait
and can dispatch any other VS1 task. Thus, when 1S1 uses pseudo page its execution under the control of V8/37C more closely resembles
its execution on a real machine. When a Fage fault occurs for an vs1 virtual machine, VM/370 ensures
(1) that the Fseudo page fault portion of handshaking is active and (2)
that the 151 virtual machine is in 2C mode and enabled for I/O interruptions. Then, V8/370 reflects the page faults to VS1 by: • Storing the virtual machine address that caused the page fault at
location X'90' (the translation exception address) • Reflecting a Frogram interruption (interruption code X'14') to VS1 • Removing the VS1 virtual machine from page and execution wait When VS1 recognizes program interruption code X'14', it places the
associated task in a wait state. VS1 can then dispatch other tasks. When the requested page is available in real storage, VM/370 reflects
the same program interruption to VS1, except that a bit in the
translation exception address field is set to one to indicate ccmFletion. VS1 removes the task from page wait, and the task is then
eligible to be dispatched.
Note: VS1 with handshaking is not designed to run in a machine that is itself running under VM/370. Otherwise,
page fault occurs, the second-level V8/370 system (18/370 dces not recognize the page fault and terminates with a
code. VM/370 virtual
when a pseudo
under VM/370) PRG020 abend Section 4. OS/VS in a Virtual Machine 111