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-ProgramSupport: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 assistCP 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 instructionsLPSW, 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 addressX'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 thanCP 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 whichECPS is available, and identifies, by process
or, the functions and instructionsECPS supports.
Performance Guidelines 39
machine, that is, a virtual machine that is running in a virtual machine.
Extended Control-Program
leged instructions, the hardware assistance that the virtual machine assist feature
provides.
ance gains that the virtual machine assist feature provides.
Expanded virtual machine assist
Virtual interval timer assist
Expanded virtual machine assist extends the hardware assistance that the virtual
machine assist feature provides for the instructions
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
control of the real processor. Virtual interval timer assist updates the virtual timer
at the same frequency hardware updates the real timer,
Thus, virtual interval timer assist updates the virtual timer more frequently than
be able to provide accounting data that is more accurate.
Figure 4 lists the processors on which
or, the functions and instructions
Performance Guidelines 39