In theory, real-time systems are provisioned based on provably sound worst-case execution times (WCETs), but in practice often only empirically derived, unsound execution-time estimates—i.e., nominal execution times (NETs)—are available since WCETs are difficult to obtain on modern hardware. NETs pose two significant challenges: First, since NETs may be exceeded at runtime, any response-time bounds derived from NETs are transitively unsound and may be violated. Second, even a minuscule NET violation can result in large, nonlinear response-time increases due to hard-to-predict, cascading scheduling effects. To explore the risk NET exceedance poses to a system’s temporal correctness, this paper provides the first general, systematic, and explainable methodology for exceedance analysis. The proposed approach supports fixed-priority (FP), earliest-deadline first (EDF), and first-in first-out (FIFO) scheduling on a uniprocessor or within a partitioned multiprocessor platform, and the full spectrum of preemption models from fully preemptive to fully non-preemptive workloads. Additionally, it produces explainable evidence in the form of tunable example traces that engineers can adjust to take system-specific expertise into account. The proposed methodology is evaluated with synthetic task sets and workloads based on an automotive benchmark, and in a case study applied to parts of the WATERS’17 industrial challenge.

Commercial off-the-shelf (COTS) multicore platforms are often used to enable the execution of mixed-criticality real-time applications. In these systems, the memory subsystem is one of the most notable sources of interference and unpredictability, with the memory controller (MC) being a key component orchestrating the data flow between processing units and main memory. The worst-case response times of real-time tasks is indeed particularly affected by memory contention and, in turn, by the MC behavior as well. This article presents FrATM2, a Framework to Automatically learn the Timing Models of the Memory subsystem. The framework automatically generates and executes micro-benchmarks on bare-metal hardware to profile the platform behavior in a large number of memory-contention scenarios. After aggregating and filtering the collected measurements, FrATM2 trains MC models to bound memory-related interference. The MC models can be used to enable response-time analysis. The framework was evaluated on an AMD/Xilinx Ultrascale+ SoC, collecting gigabytes of raw experimental data by testing tents of thousands of contention scenarios.

With heterogeneous multi-core platforms being crucial to execute the highly demanding workloads of modern applications, memory-access predictability remains a key issue for the system's safety. Many solutions have been proposed over the years, but none has been applied on a large scale. Nowadays, we are in front of an unprecedented opportunity to have an impact on commercial platforms: the Memory System Resource Partitioning and Monitoring (MPAM) specification by Arm, which describes different memory-access regulation mechanisms, presenting a valuable industrial attempt to address this issue. However, several points of the specification are described at a high level only, leaving plenty of room for interpretation to hardware manufacturers. This paper takes a close look at the memory-access regulation mechanisms in the MPAM specification and provides some detailed instantiations of such mechanisms. A fine-grained memory contention analysis is presented for each of them to finally enable a comparison of their worst-case performance.

Abstract Motivated by the increasing number of embedded applications that make use of traffic‐intensive I/O devices, this work studies the memory contention generated by I/O devices and investigates on the regulation of the bus traffic they generate by means of COTS regulators, namely the QoS‐400 by Arm. To this purpose, the behavior of the QoS‐400 regulators is analytically characterized and then, taking the Xilinx Ultrascale+ as a reference modern heterogeneous platform, a software infrastructure to control such regulators from Linux is proposed. As an experience report, this article presents the results of an extensive experimental evaluation, based on both benchmarks and microbenchmarks, aimed at validating the effectiveness of QoS‐400 regulators in predictably controlling I/O‐related memory traffic, as well as assessing the impact of the regulation on software applications and I/O devices themselves.

Modern applications are often characterized by a tight interaction with I/O devices. At the same time, many application domains are also facing a shift toward an integrated approach where multiple applications with mixed levels of safety and security need to co-exist on top of a shared hardware platform, which is typically managed by a hypervisor. This gives rise to the need for a predictable mechanism allowing multiple virtual machines to share I/O devices, while at the same time controlling contention delays when they access global memory. To deal with these shortcomings, this article proposes an I/O virtualization framework providing support for controlling the I/O-related memory contention by leveraging the ARM QoS-400 regulators. Extensive experiments are performed to compare the proposed solution with the Xen hypervisor, showing improvements up to$8\times $when controlling the I/O-related memory contention.