System Recovery Boost Enhancements

z15 machines have the option of using System Recovery Boost. When an LPAR is starting up from an IPL the Boost activates automatically and can bring online zIIP engines that were offline. These additional engines are identified as transient engines.

If PRESCPU is specified and that same LPAR is shutdown while the Boost is active the transient logical zIIP engines that were brought online by the boost will stay online when the LPAR next comes up, but they are no longer transient engines they are considered part of the normal configuration from then on until they are manually brought offline. This of course leaves additional logical engines online when they weren't expected be on.

This is problematic for multiple reasons.
In cases where customers rely on a set amount of logical engines to restrict the amount of zIIP an LPAR can use could face issues with these LPARs now having full access to all zIIPs on the CEC. This is especially important when you have a CEC that is shared with Production and nonproduction LPARs.

IBM documentation references that the IEABE proc can be used to end the Boost prior to shutdown but it is up to the customer to automate it with their own methods.

We would like to ask that the BOOST parameter be modified to add an option that would allow the customer to specify that the BOOST automatically turn off prior to LPAR shutting down. Customers that want to have the Boost shutdown at other times still have the option to use IEABE proc but this eliminates the need to come up with custom routines to specify when the IEABE proc should run and having to monitor that it completed successfully before shutting down.

Another option would be to enhance PRESCPU so that the transient engines stay flagged as transient across IPL. When the LPAR comes up and IPL boost kicks off it does not bring on additional engines and will simply turn the transient engines off once IPL BOOST ends.