If the calculated working set of the highest priority virtual machine
in the eligible list is greater than the number of page frames available
for allocation, then 15 percent of the working set for that virtual machine is calculated. If the pages required for 15 percent of the
working set are available, the virtual machine is placed on 02. otherwise, the virtual machine remains on the eligible list until there
are no other users on 01 or 02. Executable virtual machines are sorted by "dispatching priority".
This priority is calculated each time a user is dropped from a queue and
is the ratio of processor time used while in the queue to elapsed time in the queue. Infrequent processor users are placed at the top of the
list and are followed by more frequent processor users. When a
nonexecutable user becomes executable, he is placed on the queue based
on his dispatching priority. When a virtual machine completes its time slice of processor usage,
it is dropped from 02 and placed in the eligible list by user priority. When a user request in 02 enters CP command mode, it is removed from 02. the tc .i=tual .achina execution mode), it is placed in the eligible list based on user
priority.
If a user's virtual machine is not in 01 or 02, it is because: • The virtual machine is on the "eligible list," waiting to be put on 02 -- or -- • The virtual machine execution is suspended because the user is in CP mode executing CP commands To leave CP mode and return his virtual machine to the "eligible
list" for 02, the user can issue one of the CP commands that transfer
control to the virtual machine operating system for execution (for example, BEGIN, IPL, EXTERNAL, and RESTART). In CP, interactive users (01), if any, are considered for dispatching
before noninteractive users (02). This means that CMS users entering commands that do not involve disk or tape I/O operations should get fast
responses from the VM/310 system even with a large number of active
users. An installation may choose to override the CP scheduling and
dispatching scheme and force allocation of the processor resource to a
specified user, regardless of its priority or operating characteristics.
The favored execution facility allows an installation to:
1. Specify that one particular virtual machine is to receive up to a
specified percentage of processor time. 2. Specify that any number of virtual machines are to remain in the
queues at all times. Assignment of the favored execution option is
discussed in the "Preferred Virtual Machines" section.
1-12 IBM VM/310 System Logic and Problem Deteraination--Voluae 1

Functional Information The functional diagrams that follow describe the prograa logic
associated with various control program functions. Not all CP functions
are described. These functional diagrams are meant to describe the CP
functions about which you may want aore detailed inforaation if you are
debugging, modifying, or updating CP. Figure 1 describes CP initialization process.
Figures 2 and 3 describe the real and virtual I/O control blocks used
by CP in its I/O control.
Figures 4, 5, and 6 show how CP handles SVC. external, and prograa
interrupts.
The CP paging function is described in Figure 7.
The CP spooling function (both virtual and real) is described in
Figures 8 and 9.
Figure 10 shows how virtual tracing is performed.
Figure 11 shows the steps involved in translating a virtual address
to a real address and gives an example of address translation.
The functional information contained in these diagraas is intended
for system programmers and IBM Field Engineering prograa support
representatives.
CP Introduction 1-13