1. A computer program product for evaluating a response time in a computer system, wherein a plurality of units of execution are run in parallel on individual processor cores while sharing internal hardware resources, the computer program product comprising a computer readable storage medium having computer readable instructions embodied therewith, the instructions executable by a computer to cause the computer to: normalize a utilization state of the computer system with the state of parallelism of the units of execution and evaluate the utilization state, wherein normalizing the utilization state comprises obtaining a utilization state of all CPU threads of the processor cores, and calculating a normalized utilization value from the obtained utilization state of each CPU thread with reference to a case in which a number of active threads is 1; calculate an expected value of response time in a desired state of parallelism of the units of execution from the normalized utilization state on the basis of queueing theory, wherein changes in an average single-thread performance of the units of execution according to the parallel running state are taken into account; determine a degree of parallelism or a combination of degrees of parallelism at which the calculated expected value of response time is optimized as the state of parallelism of the units of execution used in the utilization state; and update the state of parallelism of the units of execution used on the basis of the calculated result of the expected value of response time in the state of parallelism, wherein the plurality of units of execution are run in parallel on the individual processor cores using a simultaneous multi-threading (SMT) function, and the expected value of response time is calculated while the SMT function is enabled.