6. DATA SOURCES › 6.8 PR/SM LPAR Concepts › 6.8.4 Interpreting PR/SM Data › 6.8.4.2 Meaning of "CPU Busy" and "CPU Wait"

6.8.4.2 Meaning of "CPU Busy" and "CPU Wait"

From the point of view of z/OS running in a logical
partition, CPU busy time is the sum of the durations of the
periods during which the logical processor is actually
executing instructions.  For shared processor wait-disabled
partitions, this is equal to the PR/SM dispatch time.  For
wait-enabled partitions, however, CPU busy time is equal to
the dispatch time minus the CPU wait time recorded in the CPU
Data section.

From the point of view of the entire complex, on the other
hand, central processor utilization does not depend on the
wait assist status.  If a logical processor is dispatched,
the central processor it uses is unavailable for other use,
whether it is actually executing instructions or is in the
wait state.  The amount of time during which the central
processor is unavailable to other partitions or for LPAR
management functions is equal to the dispatch time in both
cases.  In order to differentiate this measurement from "CPU
busy" as described previously, we can think of the dispatch
time as "CPU allocation" time.

CPU wait time in the LPAR environment can be defined as "CPU
not busy." This covers the amount of time represented by the
difference between the overall duration of the measurement
interval and CPU busy time.  For wait-disabled partitions,
this is the duration of the measurement interval minus the
dispatch time.  For wait-enabled partitions, this is the
interval duration minus the difference between the dispatch
time and the CPU wait time recorded in the CPU Data section.

The following formulas can be used to calculate processor
utilization statistics:

o  For partitions with dedicated processors

              INTERVAL - WAITTIME
   PCT_BUSY = ------------------- x 100
                   INTERVAL

   PCT_ALLC = 100 (constant)

              WAITTIME
   PCT_WAIT = -------- x 100
              INTERVAL

   PCT_NBSY = PCT_WAIT


o  For partitions with shared processors and with wait-assist
   disabled

              DISPTIME
   PCT_BUSY = -------- x 100
              INTERVAL

   PCT_ALLC = PCT_BUSY

   PCT_WAIT = 0 (constant)

              INTERVAL - DISPTIME
   PCT_NBSY = ------------------- x 100
                   INTERVAL

 
o  For partitions with shared processors and with wait-assist
   enabled

              DISPTIME - WAITTIME
   PCT_BUSY = ------------------- x 100
                   INTERVAL

              DISPTIME
   PCT_ALLC = -------- x 100
              INTERVAL

               WAITTIME
   PCT_WAIT = -------- x 100
              INTERVAL

              INTERVAL - (DISPTIME - WAITTIME)
   PCT_NBSY = -------------------------------- x 100
                          INTERVAL

where:

                                       CA MICS
label      meaning                     element
---------  --------------------------- --------
PCT_BUSY   Percent processor busy      IPUPCBS
PCT_ALLC   Percent processor allocated IPUPCDT
PCT_WAIT   Percent processor wait      IPUPCVW
PCT_NBSY   Percent not using processor IPUPCWT
INTERVAL   Measurement interval        DURATION
WAITTIME   processor wait time         IPUWTM
DISPTIME   processor dispatch time     IPUDTM