Hardware performance monitoring counters have recently received a lot of attention. They have been used by diverse communities to understand and improve the quality of computing systems: for example, architects use them to extract application characteristics and propose new hardware mechanisms; compiler writers study how generated code behaves on particular hardware; software developers identify critical regions of their applications and evaluate design choices to select the best performing implementation. We propose that counters be used by all categories of users, in particular non-experts, and we advocate that a few simple metrics derived from these counters are relevant and useful. For example, a low IPC (number of executed instructions per cycle) indicates that the hardware is not performing at its best; a high cache miss ratio can suggest several causes, such as conflicts between processes in a multicore environment.

This article explores some of the Linux architectures that support real-time characteristics and discusses what it really means to be a real-time architecture. Several solutions endow Linux with real-time capabilities, and in this article I examine the thin-kernel (or micro-kernel) approach, the nano-kernel approach, and the resource-kernel approach. Finally, I describe the real-time capabilities in the standard 2.6 kernel and show you how to enable and use them.