This paper explores the problem of how to improve the average-case performance of real-time locking protocols, preferably without significantly deteriorating worst-case performance. Motivated by the futex implementation in Linux, where uncontended lock operations under the Priority Inheritance Protocol (PIP) do not incur mode-switching overheads, we extend this concept to more sophisticated protocols; namely the PCP, the MPCP and the FMLP + . We identify the challenges involved in implementing futexes for these protocols and present the design and evaluation of their implementations in LITMUS RT , a real-time extension of the Linux kernel. Our evaluation shows substantial improvements in the uncontended case (e.g., a futex implementation of the PCP lowers lock acquisition and release overheads by up to 75% and 92%, respectively), at the expense of some increases in worst-case overhead on par with Linux's existing futex implementation.
Modern computer systems are exceedingly complex, and increasingly so. This makes it challenging for students with no background in computer systems to climb the mountain of 40 years of design, particularly within a constrained teaching timetable. Through the medium of FPGAs, we have designed an 8-week course to take students from basic digital electronics through to processor design, modern software tools, applications, system-on-chip integration and electronics manufacturing. We recount our experiences with rapidly bringing students up to speed with the modern world of computing systems, and some of the lessons we, as course designers, were taught by the process.
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