Application-level initiation of processor parameter adjustment

1. A computer implemented method for application-level initiation of processor parameter adjustment, the method comprising:

receiving, by a hypervisor in a computer system from an application running on the computer system, a request to adjust an operating parameter of a processor of the computer system, wherein the request comprises an index;

determining whether the index is listed in an index table with an associated parameter register value and whether the index is a default index that is not listed in the index table;

based on determining that the index is not listed in the index table:

determining an adjusted value for the operating parameter during execution of the application by the hypervisor; and

setting the operating parameter in a parameter register of the processor to the adjusted value by the hypervisor;

based on determining that the index is listed in the index table, setting the parameter register equal to the associated parameter register value;

based on determining that the index is a default index that is not listed in the index table;

determining an adjusted value for a plurality of operating parameters that are stored in the parameter register;

assigning an index to the application;

storing the adjusted value for the plurality of operating parameters in the index table with the assigned index; and

returning the assigned index to the application; and

executing the application according to the parameter register of the processor.

2. The method of claim 1 , further comprising writing the index and the determined adjusted value into the index table.

3. The method of claim 1 , wherein the parameter register holds values for the plurality of operating parameters, and the request specifies a subset of the plurality of operating parameters to be adjusted.

4. The method of claim 3 , wherein the plurality of operating parameters comprises a branch history algorithm, a branch history depth, a cache data prefetch depth, whether to enable store-hit-load prevention, whether to route all fixed-point operations to a fixed point unit (FXU), whether to route all loads to a load unit, an instruction prefetch depth, and a store gather window.

5. The method of claim 1 , wherein determining an adjusted value for the operating parameter during execution of the application comprises:

iterating through all possible values of the operating parameter;

measuring performance of the processor for each of the possible values by a performance monitoring unit; and

determining a value of the operating parameter that gives a highest performance of the processor.

6. A computer program product for implementing application-level initiation of processor parameter adjustment, the computer program product comprising:

a computer readable storage medium having program instructions embodied therewith, the program instructions readable by a processing circuit to cause the processing circuit to perform a method comprising:

receiving, by a hypervisor in a computer system from an application running on the computer system, a request to adjust an operating parameter of a processor of the computer system, wherein the request comprises an index;

determining whether the index is listed in an index table with an associated parameter register value and whether the index is a default index that is not listed in the index table;

based on determining that the index is not listed in the index table:

determining an adjusted value for the operating parameter during execution of the application by the hypervisor; and

setting the operating parameter in a parameter register of the processor to the adjusted value by the hypervisor;

based on determining that the index is listed in the index table, setting the parameter register equal to the associated parameter register value;

based on determining that the index is a default index that is not listed in the index table:

determining an adjusted value for a plurality of operating parameters that are stored in the parameter register;

assigning an index to the application;

storing the adjusted value for the plurality operating parameters in the index table with the assigned index; and

returning the assigned index to the application; and

executing the application according to the parameter register of the processor.

7. The computer program product of claim 6 , further comprising writing the index and the determined adjusted value into the index table.

8. The computer program product of claim 6 , wherein the parameter register holds values for the plurality of operating parameters, and the request specifies a subset of the plurality of operating parameters to be adjusted.

9. The computer program product of claim 8 , wherein the plurality of operating parameters comprises a branch history algorithm, a branch history depth, a cache data prefetch depth, whether to enable store-hit-load prevention, whether to route all fixed-point operations to a fixed point unit (FXU), whether to route all loads to a load unit, an instruction prefetch depth, and a store gather window.

10. The computer program product of claim 6 , wherein determining an adjusted value for the operating parameter during execution of the application comprises:

iterating through all possible values of the operating parameter;

measuring performance of the processor for each of the possible values by a performance monitoring unit; and

determining a value of the operating parameter that gives a highest performance of the processor.

11. A computer system for application-level initiation of processor parameter adjustment, the system comprising:

a memory; and

a processor, communicatively coupled to said memory, the computer system configured to perform a method comprising:

receiving, by a hypervisor in the computer system from an application running on the computer system, a request to adjust an operating parameter of a processor of the computer system, wherein the request comprises an index;

determining whether the index is listed in an index table with an associated parameter register value and whether the index is a default index that is not listed in the index table;

based on determining that the index is not listed in the index table:

determining an adjusted value for the operating parameter during execution of the application by the hypervisor; and

setting the operating parameter in a parameter register of the processor to the adjusted value by the hypervisor;

based on determining that the index is listed in the index table, setting the parameter register equal to the associated parameter register value;

based on determining that the index is a default index that is not listed in the index table;

determining an adjusted value for a plurality of operating parameters that are stored in the parameter register;

assigning an index to the application;

storing the adjusted value for the plurality of operating parameters in the index table with the assigned index; and

returning the assigned index to the application; and

executing the application according to the parameter register of the processor.

12. The system of claim 11 , further comprising writing the index and the determined adjusted value into the index table.

13. The system of claim 11 , wherein the parameter register holds values for the plurality of operating parameters, and the request specifies a subset of the plurality of operating parameters to be adjusted.

14. The system of claim 13 , wherein the plurality of operating parameters comprises a branch history algorithm, a branch history depth, a cache data prefetch depth, whether to enable store-hit-load prevention, whether to route all fixed-point operations to a fixed point unit (FXU), whether to route all loads to a load unit, an instruction prefetch depth, and a store gather window.