In nonpaging mode, VS1 maps virtual storage normally; that is, it
puts these functions in the high addresses of virtual storage: the JES buffer pool, VTAM workspace, RTAM area, JES routines, resident
modules, and the pageable supervisor. By minimizing the virtual
storage requirements for these functions, VS1 can provide more
problem program partition space.
The VS1 paging data set is not used in nonpaging mode. The VS1 system does not require page parameters and page packs. It is possible to execute V=R jobs in nonpaging mode. The V=R line
is a valid IPL parameter and the V=R logic within VS1 is applicable.
However, any benefits from such operation would appear to be
questionable because the entire VS1 system functions V=R in nonpaging
mode. FASTNIP automatically forces nonpaging mode when the virtual machine
storage space is 1 megabyte or largerc !2te: Although handshaking does not require nonpaging mode, may be
occasions te run a VS1 system in a virtual machine with a storage space
of 1 megabyte or larger and not use nonpaging mode. To avoid initiating
nonpaging mede, specify the virtual storage space explicitly to VS1 in
response to message IEA760A; for example: ROO, '6144'.
The following examples show whether nonpaging mode is initiated when
initializing VS1 in a V8/370 environment with handshaking. V8/370 Size = 768K OS/VS1 Virtual Storage Size = 6M IEA760A Response = 'EOB'
Nonpaging mede is not initiated, and the virtual machine storage space
is less than 1M. l: VM/370 Size = 18 OS/VS1 Virtual Storage Size = 6M IEA760A Response = 'U' Nonpaging mode is initiated, and VS1 forces the virtual machine storage
space to 1 megabyte. The VS1 system may not complete initialization
because of insufficient virtual storage space. i8/370 Size = 4M OS/iS1 Virtual Storage Size = 4M IEA760A Response = ROO, '4096' Nonpaging mode is initiated, and the explicit response happens to equal
virtual machine storage space. Section 4. as/vs in a Virtual "achine 113
VM/370 Size = 3M IEA760A Response = ROO, '6144'
Nonpaging mode is not initiated. The explicit response sets virtual
storage sFace to 6 megabytes which lS1 requires for paging space. When VM/VS handshaking is active, VS1 closes the CP spool files when
the job output from the VS1 DSO, terminator, and output writer is
complete. Once the spool files are closed, V5/370 processes them and
sends them to the real printer or punch without operator intervention.
During its job output termination processing, VS1 issues DIAGNOSE cede X'OS' instructions to pass the CP CLOSE command to VM/370 for each
CP spool file. When a nonhandshaking copy of VS1 (prior to Release 4.0) is run under VM/370, the storage considerations are the same as if VS1 were running
in native mode. The iS1 virtual storage space must be at least 512K
larger than the virtual machine storage space.
The VS1 virtual storage space is specified at VS1 system generation tiae and can be altered in response to the IPL message IEA760A SPECIFY VIRTUAL STORAGE SIZE. The virtual machine storage space is specified
initially in the VM/370 directory and can be altered by using the CP
DEFINE STORAGE command. When an operating system in a virtual machine has enabled the ETAM autopoll feature, it notifies VM/370 (via a DIAGNCSE instruction)
whenever the autopoll CCWs are modified. VM/37C then modifies the real CCWs and does not check the autopoll CCWs for modifications each time
the string is executed. This CCW change detection reduces V8/370 overhead and thereby improves the overall performance. [Qte: If the autopoll feature is disabled for VM/370 (by the SET AUTOPOLL OFF command), a performance degradation occurs. When VS1 without handshaking is run in the Ve/370 environment some
duplicaticn of function results. Because VS1 must perform certain
functions when it is run on a real machine, it continues to perform all
those functions in a VM/370 virtual machine, even though V5/370 also
provides the services. However, with handshaking, VS1 avoids using many instructions and procedures that are redundant or less efficient in
the VM/370 environment.
114 IBM VM/370 operating in a Virtual Machine
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