Enforcement Of Processing Weights; Processing Weight Management - IBM Z9 Planning Manual

resource allocated to that LP. For example, an LP defined to have two CPs on a
three-way CPC can never be allocated more than 67% of the CP resources no
matter what its processing weight.
Capping Processing Weights: The PR/SM capping function provides the
capability of limiting CPU resource usage for one or more LP. The relative
processing weight of an LP is its capping value.
A capped LP running at its cap does not have access to the CP resources that are
not utilized by other LPs. However, CP resources that are not used by a capped LP
can be used by other LPs. Equitable distribution of CP resources is maintained.
Capping values can be dynamically adjusted. The capping function can be turned
on and off, and provides the capability of specifying capping for individual LPs
without a re-IPL of the LP.
Use the Change LPAR Controls task from the CPC Operational Customization
Tasks list to change the Capped setting for the specific partition. Checking the Initial
Capping check box turns the capping function on. Select the Save Running System
push button to have this option take effect immediately for an active partition. (Save
and Change will change the running system and update the partition's profile. Save
to Profiles will not change the running system; it will just save the new definition to
the partition's profile.) Alternatively, if you do not need to change a running system,
the Customize/Delete Activation Profiles task available from the CPC Operational
Customization Tasks list can be used to open a reset or image profile to cap
processing weight for an LP. This change would take effect when the partition is
activated.
An LP's relative weight is divided by the number of shared logical CPs online for
the LP to give the share for each logical CP. The goal of the LPAR dispatcher is to
give each logical CP its share of the total relative weight. Capping is done on a
logical CP basis.
An LP's share of CP resources is determined by its weight. The combined
processing weights for all active LPs are considered to be 100% of the available
shared CP resources. The activating and deactivating of LPs changes the amount
of CP resources available to LPs, making the percentage of CP resources
requested for each active LP a relative one, and not a fixed percentage of CP
resources.
Note: If an extremely low processing weight is specified for a capped logical

Enforcement of Processing Weights

Processing Weight Management

PR/SM LPAR enforces LP processing weights as follows:
v For LPs with processor resource capping, PR/SM LPAR enforces the processing
partition, tasks such as Reset Clear, Activate, and Deactivate may fail due to
a time-out. To prevent this problem, avoid use of capping in conjunction with
low processing weight. A preferable solution is specification of a processing
weight that results in a 1/10 share (the suggested minimum) or greater of
one physical CP for a logical CP. If the extremely low weight cannot be
avoided, temporarily turn capping off for the logical partition prior to
activating, deactivating, resetting, or loading the logical partition. Restore the
cap following completion of these operations.
weights to within 3.6% of the LP's physical CP share for logical CPs entitled to
Chapter 3. Determining the Characteristics of Logical Partitions
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