Dynamic processor allocation for adaptively parallel work-stealing jobs (original) (raw)

Harnessing TCP’s burstiness with flowlet switching

Proc. 3rd ACM Workshop on Hot Topics in Networks (Hotnets- …

Abstract—TCP’s burstiness is usually regarded as harmful, or at best, inconvenient. This paper adopts a new perspective and exam- ines whether TCP’s burstiness is useful for certain applications. It shows that the burstiness ...

Efficient Queue Management for TCP Flows

2001

Packets in the Internet can experience large queueing delays during busy periods. Backbone routers are generally engineered to have large buffers, in which packets may wait as long as half a second (assuming FIFO service, longer otherwise). During congestion periods, these buffers may stay close to full, subjecting packets to long delays, even when the intrinsic latency of the path is relatively small. This paper studies the performance improvements that can be obtained by using more sophisticated packet schedulers, than are typical of Internet routers. The results show that the large buffers found in WAN routers contribute only marginally to improving router throughput, and the higher delays that come with large buffers makes them a dubious investment. The results also show that better packet scheduling algorithms can produce dramatic improvements in fairness. Using ns-2 simulations, we show that algorithms using multiple queues can significantly outperform RED and Blue, especially at smaller buffer sizes. Over a single-bottleneck link, the variance in TCP goodput using the proposed multiqueue packet schedulers is one-tenth that obtained with RED and one-fifth that obtained with Blue. Given a traffic mix of TCP flows with different roundtrip times, longer round-trip time flows achieve ¢ ¡ ¤ £ of their fair-share using multiqueue schedulers, compared to ¥ ¡ ¤ £ under RED and Blue. We observe a similar performance improvement for multi-hop paths.

A Packet Class-Based Scheme for Providing Throughput Guarantees to TCP Flows

Lecture Notes in Computer Science, 2005

TCP flows generated by applications such as the web or ftp require a minimum network throughput to satisfy users. To build this service, we propose a scheme with Admission Control (AC) using a small set of packet classes in a core-stateless network. At the ingress each flow packet is marked as one of the set of classes, and within the network, each class is assigned a different discarding priority. The AC method is based on edge-to-edge per-flow measurements, and it requires flows to be sent at a minimum rate. The scheme is able to provide different throughput to different flows and protection against nonresponsive sources. We evaluate the scheme through simulation in several network topologies with different traffic loads consisting of TCP flows that carry files of varying sizes. In the simulation, TCP uses a new algorithm to keep the short-term sending rate above a minimum value. The results prove that the scheme guarantees the throughput to accepted flows and achieves high utilization of resources, similar to the ideal results of a classical hop-by-hop AC.

Differentiated predictive fair service for TCP flows

Proceedings 2000 International Conference on Network Protocols, 2000

The majority of the traffic (bytes) flowing over the Internet today have been attributed to the Transmission Control Protocol (TCP). This strong presence of TCP has recently spurred further investigations into its congestion avoidance mechanism and its effect on the performance of short and long data transfers. At the same time, the rising interest in enhancing Internet services while keeping the implementation cost low has led to several service-differentiation proposals. In such service-differentiation architectures, much of the complexity is placed only in access routers, which classify and mark packets from different flows. Core routers can then allocate enough resources to each class of packets so as to satisfy delivery requirements, such as predictable (consistent) and fair service. In this paper, we investigate the interaction among short and long TCP flows, and how TCP service can be improved by employing a low-cost servicedifferentiation scheme. Through control-theoretic arguments and extensive simulations, we show the utility of isolating TCP flows into two classes based on their lifetime/size, namely one class of short flows and another of long flows. With such class-based isolation, short and long TCP flows have separate service queues at routers. This protects each class of flows from the other as they possess different characteristics, such as burstiness of arrivals/departures and congestion/sending window dynamics. We show the benefits of isolation, in terms of better predictability and fairness, over traditional shared queueing systems with both tail-drop and Random-Early-Drop (RED) packet dropping policies. The proposed class-based isolation of TCP flows has several advantages: (1) the implementation cost is low since it only requires core routers to maintain per-class (rather than per-flow) state; (2) it promises to be an effective traffic engineering tool for improved predictability and fairness for both short and long TCP flows; and (3) stringent delay requirements of short interactive transfers can be met by increasing the amount of resources allocated to the class of short flows.

On class-based isolation of UDP, short-lived and long-lived TCP flows

2001

The congestion control mechanisms of TCP make it vulnerable in an environment where flows with different congestionsensitivity compete for scarce resources. With the increasing amount of unresponsive UDP traffic in today's Internet, new mechanisms are needed to enforce fairness in the core of the network. We propose a scalable Diffserv-like architecture, where flows with different characteristics are classified into separate service queues at the routers. Such class-based isolation provides protection so that flows with different characteristics do not negatively impact one another. In this study, we examine different aspects of UDP and TCP interaction and possible gains from segregating UDP and TCP into different classes. We also investigate the utility of further segregating TCP flows into two classes, which are class of short and class of long flows. Results are obtained analytically for both Tail-drop and Random Early Drop (RED) routers. Class-based isolation have the following salient features: (1) better fairness, (2) improved predictability for all kinds of flows, (3) lower transmission delay for delay-sensitive flows, and (4) better control over Quality of Service (QoS) of a particular traffic type.

A cross-layer flow schedule with dynamical grouping for mitigating larger-scale TCP incast

ACM SIGAPP Applied Computing Review, 2017

Data center network (DCN), a type of network featuring low delays and high bandwidths, exchanges information rapidly through high-performance network switches. Currently, DCN provides various distributed services to satisfy user requirements. However, the size of buffers in the switches of DCNs is limited, thus causing throughput collapse when transmission control protocol (TCP) is used for multiple-to-one transmissions. Dropped packets result in additional retransmission costs and cause a substantial decrease in the efficient use of network bandwidths. Such a decrease in network performance is called a TCP incast problem. Previous studies have typically focused on modifying the original TCP or increasing additional switch hardware costs; rarely have studies focused on the existing DCN environments. Therefore, this study proposes using a cross-layer flow schedule with dynamical grouping (CLFS-DG) scheme to reduce the effect of TCP incast in DCNs. In CLSF-DG, data transmission schedu...

TCP vs. TCP: A systematic study of adverse impact of short-lived TCP flows on long-lived TCP flows

Proceedings IEEE 24th Annual Joint Conference of the IEEE Computer and Communications Societies., 2005

While earlier studies have pointed out that short-lived TCP flows (mice) may hurt long-lived TCP flows (elephants) in the long term, they provide insufficient insight for developing scenarios leading to drastic drop in throughputs of long-lived TCP flows. We have systematically developed TCP adversarial scenarios where we use short-lived TCP flows to adversely influence long-lived TCP flows. Our scenarios are interesting since, (a) they point out the increased vulnerabilities of recently proposed scheduling, AQM and routing techniques that further favor short-lived TCP flows, and (b) they are more difficult to detect when intentionally found to target long-lived TCP flows.