1. A computer-implemented method for diagnosing the performance of a computer system using a diagnostic application, comprising: providing a diagnostic application; providing an operating system (OS) kernel, said diagnostic application being configured to execute under said OS kernel in said computer system, said OS kernel having a kernel trap arrangement; providing a diagnostic monitor, said diagnostic monitor being configured to execute cooperatively with said OS kernel, said diagnostic monitor having a monitor trap arrangement; and ascertaining, using said diagnostic monitor, whether a trap encountered during execution of said diagnostic application is to be handled by said OS kernel or said diagnostic monitor; and if said trap is to be handled by said OS kernel, passing said trap to said OS kernel for handling.