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3-42
PR/SM Planning Guide
Maintaining the Same Relative Percentages of CPU Resources
To maintain the same relative percentage of CP resources requested for a capped
LP, processing weights should be readjusted immediately prior to, or immediately
after, the activation or deactivation of an LP.
Processing weight values for use when specific LPs are activated or deactivated
should be calculated in advance, and be readily available. Otherwise, it is
recommended that a convenient method be developed for changing the processing
weight values to readjust relative shares after an LP is activated or deactivated.
For example, if the sum of the weights of the active LPs totals 100, then the sum of
the relative weights of the active LPs also totals 100. This provides an easy means
for adjusting weights upon the activation or deactivation of LPs. Another good
approach to maintaining the desired share for a capped LP is to also readjust the
processing weights for LPs with the capping function turned off, as shown in
Table 3-5 for the LP ZOSTEST.
Table 3-5. Example of Maintaining Relative Weight of a Capped Logical Partition
LP Name
Status
ZVSE
A
ZOSPROD
A
ZOSTEST
A
When the sum of all the relative weights is maintained at 100, it is easy to
recalculate weights when an LP is deactivated. After deactivating ZVSE, the weight
for ZOSPROD can be changed to 64 to maintain the same relative weight of 20 for
ZOSTEST, the capped LP.
Capping in a Single Logical Partition: In order to use capping for an LP on a
CPC where there is a need for only one active LP using shared CPs, you must
define and activate a second "dummy" LP. The dummy LP must also be defined as
using shared CPs. The weights of the two LPs can be adjusted to attain the desired
cap for the one LP that will actually be used.
The "dummy" LP does not have to be capped. In most cases, the "dummy" LP does
not need to have anything IPLed into it. If nothing is IPLed into the "dummy" LP, the
"dummy" LP will not use any CP resources. In some situations where the single
capped LP runs an extremely CP-intensive workload, it may be necessary to run a
program in the "dummy" LP to smooth distribution of CP resources to the LPs. The
program can be a simple branch loop that spins to waste time. Without this program
running in the "dummy" LP, the CP-intensive, capped LP can experience a lurching
effect with its dispatched times. It will be capped to its weight properly, but it could
get all of its allotted CP resource quickly and then wait for a period of time before it
can run again.
If nothing is to be IPLed into the "dummy" LP, the "dummy" LP can be defined and
activated with no channel paths or devices. A definition with no devices is desirable
to prevent control unit logical paths from being established for the "dummy" LP. See
"Managing Logical Paths for ESCON and FICON Channels" on page 2-7.
Capping and Disabling Event-Driven Dispatching in a Single LP
Configuration: If you want to disable event-driven dispatching and enable capping
in a single LP configuration, you must do both of the following:
Four LPs Active
Weight
Capped
30
No
40
No
20
Yes
Three LPs Active
Status
Weight
Capped
D
–
A
64
A
20
–
No
Yes
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