The logical processors for a partition in HiperDispatch mode fall
into one of the following categories:
- Some of the logical processors for a partition may receive a 100%
processor share, meaning this logical processor receives an LPAR target
for 100% share of a physical processor. This is viewed as having a
high processor share. Typically, if a partition is large enough, most
of the logical partition’s share will be allocated among logical
processors with a 100% share. PR/SM™ LPAR
establishes a strong affinity between the logical processor and a
physical processor, and these processors provide optimal efficiencies
in HiperDispatch mode.
- Other logical processors may have a medium amount of physical
processor share. The logical processors would have a processor share
greater than 0% and up to 100%. These medium logical processors have
the remainder of the partition’s shares after the allocation
of the logical processors with the high share. LPAR reserves at least
a 50% physical processor share for the medium processor assignments,
assuming the logical partition is entitled to at least that amount
of service.
- Some logical processors may have a low amount, or 0%, of physical
processor share. These “discretionary” logical processors
are not needed to allow the partition to consume the physical processor
resource associated with its weight. These logical processors may
be parked. In a parked state, discretionary processors do not dispatch
work; they are in a long term wait state. These logical processors
are parked when they are not needed to handle the partition’s
workload (not enough load) or are not useful because physical capacity
does not exist for PR/SM to
dispatch (no time available from other logical partitions).
When
a partition wants to consume more CPU than is guaranteed by its share
and other partitions are not consuming their full guaranteed share,
a parked processor can be unparked to start dispatching additional
work into the available CPU cycles not being used by other partitions.
An unparked discretionary processor may assist work running on the
same processor type.
When
examining an RMF™ CPU activity
report in HiperDispatch mode, one may now see very different processing
utilizations across different logical processors of a logical partition.
For further information, refer to z/OS RMF Report Analysis.