Beginning with the 6.1 release, if you study the Collection Services database files carefully, you will discover a new field called “Scaled CPU time.”
This field in the QAPMJOBMI file is described as follows:
“Thread scaled interval CPU time used charged. The amount of scaled processing time (in microseconds) charged to this thread. The ratio of JBSCPU to JBCPU shows the current processor speed in relation to nominal processor speed.”
There’s also “Job scaled CPU time,” which is described as being “Thread scaled interval CPU time charged (in microseconds) totaled for all threads of the job within the interval…..”
In the QAPMSYSTEM file you will find:
“Scaled CPU time used (milliseconds). On some system models, the processors may operate at different speeds at different times, depending on power consumption or operating temperature. Ratio of SYSSPTU to SYSPTU shows the current processor speed in relation to nominal processor speed.”
So just what the heck is this “Scaled CPU time,” anyway?
The POWER processors support a technology called EnergyScale. EnergyScale provides the ability to control the power consumed with power-capping or power-savings modes, and when this is done, the frequency of the processor may change. It’s under these conditions that the scaled CPU time becomes important.
Scaled CPU time is based on nominal speed, so it shows what the utilization would be if the processor had been running at it’s normal speed. CPU time is based upon the current processor speed, whether it’s running at the normal speed, or faster or slower.
If the processor is slowed down in order to save energy, that’s something that can be important to be aware of if you’re concerned about performance. The scaled CPU time allows you to know whether the energy-management features have taken effect on that partition.
If you happen to have one of these particular system models that’s configured to take advantage of the power-management features, you will also discover a field on the Work with System Activity (WRKSYSACT) display: “Average CPU Rate,” which displays the ratio of scaled CPU time to CPU time.
Here are some example screen captures that show what WRKSYSACT will display under various conditions; note the change in the Average CPU rate that occurs.
This first example is POWER7 running in normal mode at 100-percent utilization:
This second example is POWER7 in Static Power Saver mode at 100-percent utilization:
This third example is POWER7 with Dynamic Power Optimizer w/Maximum Performance at 100-percent utilization:
As the example screen captures demonstrate, if the processor is running at it’s normal speed, the ratio of scaled CPU time to CPU time will be 1. However, if the processor is running at a reduced speed, you will see this ratio be less than 1. If the processor is running with maximum performance, you may see this ratio be greater than one. In the Performance Data Investigator, you will discover some of the charts include scaled CPU time as well. For example, “CPU Utilization Overview” includes a chart that displays the ratio of Scaled CPU time with CPU time.
Using the metric finder (the “Search” button on the main Investigate Data task), we can find all the charts within the Performance Data Investigator that show “Scaled CPU Time”:
If you want to know more about the IBM EnergyScale technologies, refer to these whitepapers:
- IBM EnergyScale for POWER6 Processor-Based Systems
- IBM Energyscale for POWER7 Processor-Based Systems
- IBM EnergyScale for POWER8 Processor-Based Systems
- IBM Energyscale for POWER9 Processor-Based Systems
This post was edited for currency on January 31, 2020.
This blog post was originally published on IBMSystemsMag.com and is reproduced here by permission of IBM Systems Media.