If the calculated working set of the highest priority virtual machine
in the eligible list is greater than thenumber of page frames available
for allocation, then 15 percent of the working set for that virtualmachine is calculated. If the pages required for 15 percent of the
working set are available, the virtualmachine is placed on 02. otherwise, the virtual machine remains on the eligible list until there
are no other users on01 or 02. Executable virtual machines are sorted by "dispatching priority".
This priority is calculated eachtime a user is dropped from a queue and
is the ratio of processortime used while in the queue to elapsed time in the queue. Infrequent processor users are placed at the top of the
list and are followedby more frequent processor users. When a
nonexecutable userbecomes 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 droppedfrom 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 virtualmachine 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" for02, the user can issue one of the CP commands that transfer
control to the virtualmachine 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). Thismeans that CMS users entering commands that do not involve disk or tape I/O operations should get fast
responsesfrom 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 processortime. 2. Specify that any number of virtual machines are to remain in the
queues at alltimes. Assignment of the favored execution option is
discussed in the "PreferredVirtual Machines" section.
1-12IBM VM/310 System Logic and Problem Deteraination--Voluae 1
in the eligible list is greater than the
for allocation, then 15 percent of the working set for that virtual
working set are available, the virtual
are no other users on
This priority is calculated each
is the ratio of processor
list and are followed
nonexecutable user
on his dispatching priority.
it is dropped
priority.
If a user's virtual
list" for
control to the virtual
before noninteractive users (02). This
responses
users.
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.
specified percentage of processor
queues at all
discussed in the "Preferred
1-12