IBM Z9, Руководство по планированию

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coupling facility logical CP has 50% or more of a physical CP resource. If you
have less than a full physical CP allocated to the coupling facility logical CP,
this will result in elongation of response times .
Examine the RMF Coupling Facility Activity Report and tune the coupling
facility LP weight until your performance requirements are met.
Note: When examining the RMF Coupling Facility Activity Report, you may
see elongated average response times. Usually, these are
accompanied with high standard deviations as well. This indicates most
requests are in the expected range with an occasional very elongated
response that throws the average off.
– Give more weight to the coupling facility LP for functions that have more
stringent responsiveness requirements. For example, you can set the coupling
facility weight higher for coupling facility exploiter functions such as IMS/IRLM.
For IMS/IRLM, you may want to set the weight of the coupling facility LP so
that each coupling facility logical CP runs almost dedicated. For example, you
may want to set a weight that will give each coupling facility logical CP 95%
or more of physical CP resources. In another case, if the CF contains
structures which are using System Managed Duplexing, you should set the
weight of the coupling facility LP so that the coupling facility CP has at least
95% of a physical CP. If the coupling facility has less than 95% of a physical
CP, there is a possibility that response from the partner of the duplexed
structure will timeout and the duplexing of that structure will cease.
– Less weight may be required for coupling facility exploiter functions, such as
the JES2 Checkpoint data set. If your coupling facility is being used
exclusively as a JES2 checkpoint, your coupling facility responsiveness
requirements may be less stringent. If this is the case, try decreasing the
weight of the coupling facility LP so that each coupling facility logical CP
receives, for example, 40-50% of physical CP resources.
– As the total traffic (requests per second) to the coupling facility increases,
there is a greater need for real coupling facility CP time. To a point, the
increase in traffic may not require an increase in the coupling facility LP
weight. This is because coupling facility active wait time turns into coupling
facility busy time. You must monitor coupling facility utilization and adjust the
LP weight to help ensure that your performance requirements are being met.
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Even in a test environment, the above guidelines should be followed. Optimally, a
weight resulting in approximately 50% or more of a processor should be made
for each coupling facility logical processor. Failure to provide sufficient weight
to a coupling facility may result in degraded performance, loss of
connectivity, and possible loss of coupling links due to time-outs. Dynamic
CF dispatching must not be disabled. Dynamic CF dispatching is automatically
enabled by default for coupling facility LPs that are using shared general purpose
CPs. Additionally, processor resource capping of the coupling facility logical
partition(s) logical CPs must not be enabled.
Considerations for Coupling Facilities Running on Uniprocessor
Models
On a uniprocessor or smaller machine, IBM strongly recommends that coupling
facility LPs should not share general purpose CPs with non-CF workloads (for
example, z/OS), even in a test environment. Such a configuration carries with it
significant risks of degraded performance, loss of connectivity, and possible
loss of coupling links due to time-outs and must not be used for a production
level system. For production configurations, IBM strongly recommends using one
or more internal coupling facility (ICFs) CPs for the coupling facility LPs.
Chapter 3. Determining the Characteristics of Logical Partitions
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