Dynamic CPU capacity

Dynamic CPU capacity provides the capability to expand and collapse I-streams automatically based on the utilization of the in-use I-streams. In addition, I-stream controls are provided for you to restrict the use of I-streams to the number that is immediately needed and add capacity when needed without an outage.

Plan for dynamic CPU capacity

To use dynamic CPU capacity efficiently, ensure that you plan for the maximum capacity that you will need until the next scheduled outage or, if there is no scheduled outage, for the life of the machine. Consider the maximum number of physical I-stream engines (CPUs) and the maximum number of logical I-streams for each LPAR that will be needed.

After the z/TPF system is initially installed or restarted, all I-streams that are defined to the LPAR are available to be used. You can use I-stream controls to manage how many I-streams are actually used as your capacity needs change.

Use I-stream controls

When I-streams for each LPAR are available to be used, you can set the I-stream cap with the number of I-streams that are immediately needed. Application work is distributed to I-streams that have numbers less than or equal to the I-stream cap. When more capacity is needed, you can change the I-stream cap without an outage.

You can enable HiperDispatch to ensure that the minimal number of I-streams is used. When HiperDispatch is being used, the z/TPF system checks the utilization of in-use I-streams every second to determine whether to expand or collapse the in-use I-streams based on the I-stream cap. You can use the HiperDispatch setting only when the z/TPF system is running on a shared LPAR.

The I-stream floor prevents the z/TPF system from collapsing below a specified I-stream number.

You can use the ZMISS command to manage the I-stream controls.

Use I-stream cap logging

You can use I-stream cap logging to periodically collect the status of I-stream controls, utilization of collapsed I-streams, and other system information. The collected data is stored in the I-stream cap log files, and a I-stream cap report is generated based on the I-stream cap log files.

I-stream cap logging is enabled when the number of days to keep I-stream cap log files is not zero. Use the KEEP on the ZMISS command to set the number of days to keep I-stream cap log files. For example, the following command sets the number of days to 45: ZMISS SET LOG KEEP-45

Test collapse

You can enter the ZSTRC command with the ALTER and TESTCLPS parameters specified to simulate the behavior of HiperDispatch when the z/TPF system is running as a guest under z/VM®. When you enter this command, the z/TPF system expands and collapses I-streams as if HiperDispatch is in use.