The use of microcode instrumentation for development, debugging and tuning of operating system kernels

Abstract

We have developed a tool based on microcode modifications to a VAX 8600 which allows a wide variety of operating system measurements to be taken with minimal perturbation and without the need to modify any operating system software. A trace of interrupts, exceptions, system calls and context switches is generated as a side-effect to normal execution. In this paper we describe the tool we have developed and present some results we have gathered under both UNIX 4.3 BSD and VAX/VMS V4.5. We compare the process fork behavior of two different command shells under UNIX, look at context switch rates for interactive and batch workloads and generate a histogram for network interrupt service time.