2. PERFORMANCE REPORTING ANALYSIS › 2.7 Graphic Analysis › 2.7.5 Paging Graphs

2.7.5 Paging Graphs

When central and expanded storage are sufficiently large, an
MVS system may do little or no paging.  As workloads grow and
applications are enhanced, contention for central and
expanded storage may cause MVS to make use of auxiliary
storage paging files especially established for this purpose.
A limited amount of paging can provide an excellent cushion
for central and expanded storage.

However, each time MVS must demand that a page be transferred
into central storage from DASD, this represents a dramatic
increase in execution time.  If the processor attempts to
execute an instruction or refers to data that is not in
processor storage but has been paged out to auxiliary
storage, a processor page fault will occur.  MVS will delay
the task attempting to execute until the instruction or data
it refers to has been moved into central storage.  Then MVS
will mark the task dispatchable and, depending on the
priority of this task relative to other tasks in the system,
the task will eventually continue.  Thus, the task
temporarily runs at the relatively slow speed of DASD I/O
instead of at the electronic speed of the processor.  The
task switching that takes place can also tend to pollute the
processor's high speed cache, further degrading performance.

Especially for critical workloads for which you have service
level objectives or service level agreements, you need to be
assured that demand paging levels are tracked and managed.

This section discusses the following graphic analyses:

    1 - Response Time for Page Data Set Type
    2 - Response Time for Local Page Data Sets
    3 - Demand Page Rates by Performance Group/Svc Class
    4 - Percent Busy for Local Page Data Sets
    5 - Demand Page Rates by Workload Type-Bar Chart
    6 - Demand Page Rates by Workload Type-Pie Chart