The Virtual Machine Assist Feature is not available to a second-level virtual
machine, that is, a virtual machine that is running in a virtual machine.
Extended Control-Program Support:VM/370 (ECPS) Extended Control-Program Support:VM/370 (ECPS) extends, for specific privi­
leged instructions, the hardware assistance that the virtual machine assist feature
provides. ECPS also provides hardware assistance for frequently used VM/SP functions. The use of ECPS improves VM/SP performance beyond the perform­
ance gains that the virtual machine assist feature provides. ECPS consists of three functions: CP assist
Expanded virtual machine assist
Virtual interval timer assist CP assist provides hardware assistance for frequently used paths of specific CP functions.
Expanded virtual machine assist extends the hardware assistance that the virtual
machine assist feature provides for the instructions LPSW, STNSM, STOSM, and
SSM. In addition, expanded virtual machine assist provides hardware assistance for
certain other privileged instructions.
Virtual interval timer assist provides hardware updating of the virtual interval timer
at virtual address X'SO'. Timer updating occurs only while the virtual machine is in
control of the real processor. Virtual interval timer assist updates the virtual timer
at the same frequency hardware updates the real timer, 300 times per second.
Thus, virtual interval timer assist updates the virtual timer more frequently than CP updates it. Because the timer is updated more frequently, accounting routines may
be able to provide accounting data that is more accurate. ECPS does not support the same functions and instructions on all processors.
Figure 4 lists the processors on which ECPS is available, and identifies, by process­
or, the functions and instructions ECPS supports.
Performance Guidelines 39

135-3, 138, 145-3 3031 Functions and Instructions 148,4341 3031AP 4331
CP Assist X X • Get free space (DMKFRE) X X • Release free space (DMKFRE) X X • Lock a page (DMKPTR) X X • Unlock a page (DMKPTR) X X • Test page status (DMKCCW) X X • Test page status and
lock (DMKCCW) X X • Store ECPS identification X X X • SVC 8 (LINK) X X X • SVC 12 (RETURN) X X X • Scan for changed shared
pages (DMKVMA) X X X • Locate virtual 110 control
block (DMKSCN) X X • Invalidate page table (DMKV AT) X X • Invalid segment
table (DMKV AT) X X • Untranslate CSW (DMKUNT) X • Free CCW storage (DMKUNT) X • Locate real 110 control
block (DMKSCN) X • Common CCW command
processing (DMKCCW) X • Decode first CCW (DMKCCW) X • Decode following CCW (DMKCCW) X • Main entry to dispatch (DMKDSP) X • Dispatch a block or a virtual
machine (DMKDSP) X
Expanded Virtual Machine Assist • LPSW X • STNSM X • STOSM X • SSM X • PTLB X • SIO X • SPT • SCKC X • STPT • TCH X X · DIAGNOSE X X
Virtual Interval Timer Assist X X X
Figure 4. Functions and Instructions that ECPS Supports 4'0 VM/SP System Programmer's Guide