Why Does Flow Director Cause Packet Reordering?

Intel Ethernet Flow Director is an advanced network interface card (NIC) technology. It provides the benefits of parallel receive processing in multiprocessing environments and can automatically steer incoming network data to the same core on which its application process resides. However, our analysis and experiments show that Flow Director cannot guarantee in-order packet delivery in multiprocessing environments. Packet reordering causes various negative impacts. E.g., TCP performs poorly with severe packet reordering. In this paper, we use a simplified model to analyze why Flow Director can cause packet reordering. Our experiments verify our analysis

Nearest neighbor affinity scheduling in heterogeneous multi-core architectures

Asymmetric or heterogeneous multi-core (AMC) architectures have definite performance, performance per watt and fault tolerance advantages for a wide range of workloads. We propose a 16 core AMC architecture mixing simple and complex cores, and single and multiple thread cores of various power envelopes. A priority-based thread scheduling algorithm is also proposed for this AMC architecture. Fairness of this scheduling algorithm vis-a-vis lower priority thread starvation, and hardware and software requirements needed to implement this algorithm are addressed. We illustrate how this algorithm operates by a thread scheduling example. The produced schedule maximizes throughput (but is priority-based) and the core utilization given the available resources, the states and contents of the starting queues, and the threads' core requirement constraints. A simulation model simulates 6 scheduling algorithms which vary in their support of core affinity and thread migration. The simulation results that both core affinity and thread migration positively effect the completion time and that the nearest neighbor scheduling algorithm outperforms or is competitive with the other algorithms in all considered scenariosFacultad de Informátic

Cache-affinity scheduling for fine grain multithreading

Cache utilisation is often very poor in multithreaded applications, due to the loss of data access locality incurred by frequent context switching. This problem is compounded on shared memory multiprocessors when dynamic load balancing is introduced and thread migration disrupts cache content. In this paper, we present a technique, which we refer to as ‘batching’, for reducing the negative impact of fine grain multithreading on cache performance. Prototype schedulers running on uniprocessors and shared memory multiprocessors are described, and finally experimental results which illustrate the improvements observed after applying our techniques are presented.peer-reviewe

Challenges Using Linux as a Real-Time Operating System

Human-in-the-loop (HITL) simulation groups at NASA and the Air Force Research Lab have been using Linux as a real-time operating system (RTOS) for over a decade. More recently, SpaceX has revealed that it is using Linux as an RTOS for its Falcon launch vehicles and Dragon capsules. As Linux makes its way from ground facilities to flight critical systems, it is necessary to recognize that the real-time capabilities in Linux are cobbled onto a kernel architecture designed for general purpose computing. The Linux kernel contain numerous design decisions that favor throughput over determinism and latency. These decisions often require workarounds in the application or customization of the kernel to restore a high probability that Linux will achieve deadlines