On service guarantees of fair-queueing schedulers in real systems

Abstract In most systems, fair-queueing packet schedulers are the algorithms of choice for providing bandwidth and delay guarantees. These guarantees are computed assuming that the scheduler is directly attached to the transmit unit with no interposed buffering, and, for timestamp-based schedulers, that the exact number of bits transmitted is known when timestamps need to be updated. Unfortunately, both assumptions are unrealistic. In particular, real communication devices normally include FIFO queues (possibly very deep ones) between the scheduler and the transmit unit. And the presence of these queues does invalidate the proofs of the service guarantees of existing timestamp-based fair-queueing schedulers. In this paper we address these issues with the following two contributions. First, we show how to modify timestamp-based, worst-case optimal and quasi-optimal fair-queueing schedulers so as to comply with the presence of FIFO\queues, and with uncertainty on the number of bits transmitted. Second, we provide analytical bounds of the actual guarantees provided, in these real-world conditions, both by modified timestamp-based fair-queueing schedulers and by basic round-robin schedulers. These results should help designers to make informed decisions and sound tradeoffs when building systems

Is subclinical cardiovascular disease linked with periodontal disease in diabetic and non-diabetic subjects?

: Periodontal disease leads to a systemic hyper-inflammatory state that might impair other co-morbidities including cardiovascular disease. Evidence-based findings showed that periodontitis may be linked with subclinical signs of cardiovascular diseases such as arterial stiffness. Nevertheless, some contrasting results have been reported over the years. A cross-sectional study regarding the relationship between periodontal disease and subclinical cardiovascular diseases, in non-diabetic and diabetic individuals, has been recently published. Therefore, the aim of this commentary is to give an in-depth on this topic

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

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)

Packet Classification via Improved Space Decomposition Techniques

P ack et Classification is a common task in moder n Inter net r outers. The goal is to classify pack ets into "classes" or "flo ws" according to some ruleset that looks at multiple fields of each pack et. Differ entiated actions can then be applied to the traffic depending on the r esult of the classification. Ev en though rulesets can be expr essed in a r elati v ely compact way by using high le v el languages, the r esulting decision tr ees can partition the sear ch space (the set of possible attrib ute v alues) in a potentially v ery lar ge ( and mor e) number of r egions. This calls f or methods that scale to such lar ge pr oblem sizes, though the only scalable pr oposal in the literatur e so far is the one based on a F at In v erted Segment T r ee [1 ]. In this paper we pr opose a new geometric technique called G-filter f or pack et classification on dimensions. G-filter is based on an impr o v ed space decomposition technique. In addition to a theor etical analysis sho wing that classification in G-filter has time complexity and slightly super -linear space in the number of rules, we pr o vide thor ough experiments sho wing that the constants in v olv ed ar e extr emely small on a wide range of pr oblem sizes, and that G-filter impr o v e the best r esults in the literatur e f or lar ge pr oblem sizes, and is competiti v e f or small sizes as well

Smell and taste dysfunction after covid-19

The sense of smell is an ancient and vital perception in mammals, with the olfactory receptor gene family making up 1% of the mammalian genome, and the human olfactory system being able to discriminate among thousands of airborne chemicals at concentrations below the detection limits of the most complex analytical systems. However, people only realise the importance of smell when it is lost. The covid-19 pandemic has put both smell and taste disturbances in the spotlight because of the functional impact and severe distress caused by the loss of these senses, their fundamental diagnostic value, and, more recently, the high rate of long term dysfunction. The linked meta-analysis by Tan and colleagues (doi:10.1136/bmj-2021-069503) gives a clear picture of the challenge humans face. About 5% of people report smell and taste dysfunction six months after covid-19, and, given that an estimated 550 million cases of covid-19 have been reported worldwide as of July 2022, large numbers of patients will be seeking care for these disabling morbidities. Health systems should therefore be ready to provide support to these patients who often report feeling isolated when their symptoms are overlooked by clinicians

Antibiotic resistance spread potential in urban wastewater effluents disinfected by UV/H2O2 process

Urban wastewater treatment plants (UWTPs) are among the main hotspots of antibiotic resistance (AR) spread into the environment and the role of conventional and new disinfection processes as possible barrier to minimise the risk for AR transfer is presently under investigation. Accordingly, the aim of this work was to evaluate the effect of an advanced oxidation process (AOP) (specifically UV/H2O2) on AR transfer potential. UV/H2O2 disinfection experiments were carried out on real wastewater samples to evaluate the: i) inactivation of total coliforms, Escherichia coli and antibiotic resistant E. coli as well as ii) possible removal of target antibiotic resistance genes (ARGs) (namely, blaTEM, qnrS and tetW). In particular, DNA was extracted from both antibiotic resistant E. coli bacterial cells (intracellular DNA), grown on selective culture media, and the whole water suspension (total DNA) collected at different treatment times. Polymerase chain reaction (PCR) assay was performed to detect the absence/presence of the selected ARGs. Real Time quantitative Polymerase Chain Reaction (qPCR) was used to quantify the investigated ARGs in terms of copiesmL(-1). In spite of the bacterial inactivation and a decrease of ARGs in intracellular DNA after 60min treatment, UV/H2O2 process was not effective in ARGs removal from water suspension (total DNA). Particularly, an increase up to 3.7×10(3)copiesmL(-1) (p>0.05) of blaTEM gene was observed in total DNA after 240min treatment, while no difference (p>0.05) was found for qnrS gene between the initial (5.1×10(4)copiesmL(-1)) and the final sample (4.3×10(4)copiesmL(-1)). On the base of the achieved results, the investigated disinfection process may not be effective in minimising AR spread potential into the environment. The death of bacterial cells, which results in DNA release in the treated water, may pose a risk for AR transfer to other bacteria present in the receiving water body