Measuring Unix Kernel Performance

We present accurate, low-level measurements of process preemption, interrupt handling and memory system performance of a UNIX 1 workstation. To gather this data, we use PAMs (Programmable Active Memory). These are fast, general purpose, bit-level programmable co-processors based on field programmable gate arrays. They are mapped to part of the system address space and appear to the CPU as memory, much like memory-mapped I/O devices. PAMs are primarily aimed at computationally intensive problems, where wide, application specific datapaths can offer great speedups over software. By contrast, in this application we rely on the realtime, concurrent aspects of a PAM that is relatively modest in terms of computational resources. Starting with a simple 25MHz counter, we describe a series of measurement devices built to answer specific questions about low-level system performance. Many of the devices are active in that they provoke the events they seek to measure. Our measurement techniques ..