Measure Reference Manual

Usage Notes for All CPU Entities
• Unlike counters for other entity types, CPU counters are allocated and initialized only when
the CPU is loaded. The counters are not reinitialized at the start of each measurement. Thus,
the CPU counter provides an overview of system performance over an extended period.
CPU counters can direct you to potential problems that you can examine in greater detail
using other entities. In particular, the PROCESS CPU-BUSY-TIME counter measures the time
spent executing specific processes. (The PROCESS CPU-NUM field lets you match processes
to CPUs.)
• For more information on system operation (how the system performs I/O, executes processes,
does paging, and so on), see the appropriate system description manual.
Usage Notes for J-Series CPU Entities
In J06.13 and later RVUs, it is possible to dynamically increase the number of enabled IPUs/CPU.
If a CPU measurement is active while such a change takes place, Measure automatically stops the
measurement and then re-starts the measurement with the new IPU count. This behavior ensures
that scaling calculations that are made for RATE ON are correct for all records. However, if TOTALS
records with RATE ON are requested, the values will not be reliable.
It is recommended that if CPU TOTALS records with RATE ON are important to you, then all CPU
measurements should be stopped before any change of enabled IPUs/CPU takes place. The CPU
measurements can then be re-started after the change is complete. This way, all the records in the
data files will be based on the same number of enabled IPUs.
Active reads are special cases, because they use the allocation timestamps (essentially the times
when the CPUs were last re-loaded), and not the timestamps when the measurements started, to
calculate the delta times in the external records and hence the RATE ON values for MEASCOM.
To make these calculations accurate for most counters during a change in IPU count, the original
allocation timestamps are saved in the internal counter records and these timestamps are used to
create the external records.
However, the IPU scaling performed for some counter fields may not be correct, because part of
the counter value would need to be scaled with the old IPU count, and part of it with the new IPU
count. It is also possible that several changes in IPUs/CPU have occurred after the CPUs were
re-loaded. As a result, even though the values in the external records returned by the Measure APIs
are correct, the following CPU counter fields will not be correctly displayed by MEASCOM for the
LISTACTIVE command with RATE ON if a change in IPUs/CPU has taken place:
• ACCEL-BUSY-TIME
• CPU-BUSY-TIME
• INTR-BUSY-TIME
• NATIVE-BUSY-TIME
• PROCESS-OVHD
• TNS-BUSY-TIME
If the LISTACTIVE command is issued with the FOR specification, the displayed values will be
correct, unless a change in IPUs/CPU takes place between the beginning and the end of the time
period.
The only way to rectify the scaling problems with the active reads is to re-load the CPUs.
176 Entities and Counters