Very high speed link emulation with TLEM

In this work we discuss the limitations of link emulators based on conventional network stacks, and present our alternative architecture called TLEM, which is designed to address current high speed links and be open to future speed improvements. TLEM is structured as a pipeline of stages, implemented with separate threads and with limited interactions with each other, so that high performance can be achieved. Our emulator can handle bidirectional traffic at speeds of over 18 Mpps (64 byte packets) and 40 Gbit/s (1500 byte packets) per direction even with large emulation delays. Even higher performance can be achieved with shorter delays, as the workload fits better into the L3 cache of the system. TLEM is distributed as BSD-licensed opensource as part of the netmap distributions, and runs on any system that supports netmap (this includes FreeBSD, Linux and now even Windows)

Flexible virtual machine networking using netmap passthrough

The rising interest in Network Function Virtualization (NFV) requires Virtual Machines (VMs) to operate with diversified networking workloads, from traditional, bulk TCP transfers to novel ones featuring extremely high packet rates. In response, researchers have explored and proposed new solutions for high performance VM networking, including optimizations to virtual network adapters (such as VirtIO) to support high speed bulk traffic, and alternative frameworks for userspace networking and physical or virtual passthrough. To date, we are still missing a comprehensive solution that supports such extreme workloads across multiple operating systems and hypervisors, while at the same time addressing other requirements such as ease of configuration, operating system independence, scalability and isolation. In this paper we present ptnet, an approach to network I/O virtualization that provides high performance for both traditional TCP/IP and high packet rate applications. ptnet leverages the features of the netmap framework (including virtualization and passthrough support), and defines a simple yet performant network device model that can be easily supported in different operating systems and hypervisors. We prove the effectiveness of our approach by comparing ptnet's performance with one of the state of the art I/O virtualization solutions, namely VirtIO on Linux and QEμKVM. ptnet is available under a BSD license as part of the netmap distributions on github

A Study of I/O Performance of Virtual Machines

In this study, we investigate some counterintuitive but frequent performance issues that arise when doing high-speed networking (or I/O in general) with Virtual Machines (VMs). VMs use one or more single-producer/single-consumer systems to exchange I/O data (e.g. network packets) with their hypervisor. We show that when the producer and the consumer process packets at different rates, the high cost required for synchronization (interrupts and ‘kicks’) may reduce throughput of the system well below the slowest of the two parties; moreover, accelerating the faster party may cause the throughput to decrease. Our work provides a model for throughput, efficiency and latency of producer/consumer systems when notifications or sleeping are used as a synchronization mechanism; identifies different operating regimes depending on the operating parameters; validates the accuracy of our model against a VirtIO-based prototype, taking into account most of the details of real-world deployments; provides practical and robust strategies to maximize throughput and minimize energy while keeping the latency under control, without depending on precise timing measurements nor unreasonable assumptions on the system’s behavior. The study is particularly interesting for Network Function Virtualization deployments, where high-rate producer/consumer systems in virtualized environments are the core components

Using abstract interpretation to add type checking for interfaces in Java bytecode verification

AbstractJava interface types support multiple inheritance. Because of this, the standard bytecode verifier ignores them, since it is not able to model the class hierarchy as a lattice. Thus, type checks on interfaces are performed at run time. We propose a verification methodology that removes the need for run-time checks. The methodology consists of: (1) an augmented verifier that is very similar to the standard one, but is also able to check for interface types in most cases; (2) for all other cases, a set of additional simpler verifiers, each one specialized for a single interface type. We obtain these verifiers in a systematic way by using abstract interpretation techniques. Finally, we describe an implementation of the methodology and evaluate it on a large set of benchmarks

Heuristic search for equivalence checking

Equivalence checking plays a crucial role in formal verification since it is a natural relation for expressing the matching of a system implementation against its specification. In this paper, we present an efficient procedure, based on heuristic search, for checking well-known bisimulation equivalences for concurrent systems specified through process algebras. The method tries to improve, with respect to other solutions, both the memory occupation and the time required for proving the equivalence of systems. A prototype has been developed to evaluate the approach on several examples of concurrent system specifications

VALE, a switched ethernet for virtual machines

With the use of virtual machines becoming more and more popular, the need for high performance communication between them also grows. Past solutions have seen the use of hardware assistance, in the form of “PCI passthrough”(dedicating parts of physical NICs to each virtual machine) and even bouncing traffic through physical switches to handle data forwarding and replication. In this paper we show that, with a proper design, very high speed communication between virtual machines can be implemented completely in ..

CFD Simulation of Binary Fluidized Mixtures: Effects of Restitution Coefficient and Spatial Discretization Methods

The work focuses on the CFD simulation of fluidized bidisperse solid particles with same density and different size. We successfully predicted the minimum superficial gas velocity required to steadily fluidize the particles by employing a second-order upwind spatial discretization method and a non-ideal value of the restitution coefficient

Glucometer Usability for 65+ Type 2 Diabetes Patients: Insights on Physical and Cognitive Issues

Background: Self-monitoring of blood glucose (SMBG) is of paramount relevance for type 2 diabetes mellitus (T2DM) patients. However, past evidence shows that there are physical and cognitive issues that might limit the usage of glucometers by T2DM patients aged 65 years and over. Objective: Our aim was to investigate the physical and cognitive issues related to the usage of glucometers by T2DM patients aged 65 years and over. Materials and Methods: The extant literature was analysed to define an original framework showing the logical nexus between physical and cognitive issues and quality of life. Then we collected evidence addressing the specific case of the Accu-Chek® Instant glucometer produced by Roche Diabetes Care GmbH, which implements new features claiming to improve usability. We conducted 30 interviews with T2DM patients aged 65 years and over, three interviews with senior nurses, and a focus group with three senior physicians and three senior nurses. Results: From the interviews, both patients and nurses declared that they were generally satisfied with the Accu-Chek® Instant glucometer’s characteristics. In the focus group, the results were commented on and, in the light of some diverging answers, improvements have been set up for future implementation. Conclusions: Our study produces evidence and future suggestions about the usage of glucometers by type 2 diabetes patients aged 65 years and over

Different FDG-PET metabolic patterns at single-subject level in the behavioral variant of fronto-temporal dementia.

BACKGROUND: The diagnosis of probable behavioral variant of fronto-temporal dementia (bvFTD) according to current criteria requires the imaging evidence of frontal and/or anterior temporal atrophy or hypoperfusion/hypometabolism. Different variants of this pattern of brain involvement may, however, be found in individual cases, supporting the presence of heterogeneous phenotypes. OBJECTIVE: We examined in a case-by-case approach the FDG-PET metabolic patterns of patients fulfilling clinical criteria for probable bvFTD, assessing the presence and frequency of specific FDG-PET features. MATERIALS AND METHODS: Fifty two FDG-PET scans of probable bvFTD patients were retrospectively analyzed together with clinical and neuropsychological data. Neuroimaging experts rated the FDG-PET hypometabolism maps obtained at the single-subject level with optimized voxel-based Statistical Parametric Mapping (SPM). The functional metabolic heterogeneity was further tested by hierarchical cluster analysis and principal component analysis (PCA). RESULTS: Both the SPM maps and cluster analysis identified two major variants of cerebral hypometabolism, namely the "frontal" and the "temporo-limbic", which were correlated with different cognitive profiles. Executive and language deficits were the cognitive hallmark in the "frontal" subgroup, while poor encoding and recall on long-term memory tasks was typical of the "temporo-limbic" subgroup. DISCUSSION: SPM single-subject analysis indicates distinct patterns of brain dysfunction in bvFTD, coupled with specific clinical features, suggesting different profiles of neurodegenerative vulnerability. These findings have important implications for the early diagnosis of bvFTD and for the application of the recent international consensus criteria