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 towards 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 paper 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 8x when controlling the I/O-related memory contention.

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.