2,061 research outputs found
Work-Conserving Distributed Schedulers
Buffered multistage interconnection networks offer one of the most scalable and cost-effective approaches to building high capacity routers and switches. Unfortunately, the performance of such systems has been difficult to predict in the presence of the extreme traffic conditions that can arise in Internet routers. Recent work introduced the idea of distributed scheduling, to regulate the flow of traffic in such systems. This work demonstrated (using simulation and experimental measurements) that distributed scheduling can en-able robust performance, even in the presence of adversarial traffic patterns. In this paper, we show that appropriately designed distributed scheduling algorithms are provably work-conserving for speedups of 2 or more. Two of the three algorithms presented were inspired by algorithms previously developed for crossbar scheduling. The third has no direct counterpart in the crossbar scheduling context. In our analysis, we show that distributed schedulers based on blocking flows in small-depth acyclic flow graphs can be work-conserving, just as certain crossbar schedulers based on maximal bipartite matchings have been shown to be work-conserving. We also study the performance of practical variants of the work-conserving algorithms with speedups less than 2, using simulation. These studies demonstrate that distributed scheduling ensures excellent performance under extreme traffic conditions for speedups of less than 1.5
Instability in Stochastic and Fluid Queueing Networks
The fluid model has proven to be one of the most effective tools for the
analysis of stochastic queueing networks, specifically for the analysis of
stability. It is known that stability of a fluid model implies positive
(Harris) recurrence (stability) of a corresponding stochastic queueing network,
and weak stability implies rate stability of a corresponding stochastic
network. These results have been established both for cases of specific
scheduling policies and for the class of all work conserving policies.
However, only partial converse results have been established and in certain
cases converse statements do not hold. In this paper we close one of the
existing gaps. For the case of networks with two stations we prove that if the
fluid model is not weakly stable under the class of all work conserving
policies, then a corresponding queueing network is not rate stable under the
class of all work conserving policies. We establish the result by building a
particular work conserving scheduling policy which makes the associated
stochastic process transient. An important corollary of our result is that the
condition , which was proven in \cite{daivan97} to be the exact
condition for global weak stability of the fluid model, is also the exact
global rate stability condition for an associated queueing network. Here
is a certain computable parameter of the network involving virtual
station and push start conditions.Comment: 30 pages, To appear in Annals of Applied Probabilit
Bits Through Bufferless Queues
This paper investigates the capacity of a channel in which information is
conveyed by the timing of consecutive packets passing through a queue with
independent and identically distributed service times. Such timing channels are
commonly studied under the assumption of a work-conserving queue. In contrast,
this paper studies the case of a bufferless queue that drops arriving packets
while a packet is in service. Under this bufferless model, the paper provides
upper bounds on the capacity of timing channels and establishes achievable
rates for the case of bufferless M/M/1 and M/G/1 queues. In particular, it is
shown that a bufferless M/M/1 queue at worst suffers less than 10% reduction in
capacity when compared to an M/M/1 work-conserving queue.Comment: 8 pages, 3 figures, accepted in 51st Annual Allerton Conference on
Communication, Control, and Computing, University of Illinois, Monticello,
Illinois, Oct 2-4, 201
Heart-like fair queuing algorithms (HLFQA)
We propose a new family of fair, work conserving traffic scheduling mechanisms that imitate the behavior of the human heart in the cardiovascular system. The algorithms have MAX (where MAX is the maximum packet size) fairness and O(log N) complexity and thus compare favorably with existing algorithms. The algorithms are simple enough to be implemented in hardwar
Enabling Work-conserving Bandwidth Guarantees for Multi-tenant Datacenters via Dynamic Tenant-Queue Binding
Today's cloud networks are shared among many tenants. Bandwidth guarantees
and work conservation are two key properties to ensure predictable performance
for tenant applications and high network utilization for providers. Despite
significant efforts, very little prior work can really achieve both properties
simultaneously even some of them claimed so.
In this paper, we present QShare, an in-network based solution to achieve
bandwidth guarantees and work conservation simultaneously. QShare leverages
weighted fair queuing on commodity switches to slice network bandwidth for
tenants, and solves the challenge of queue scarcity through balanced tenant
placement and dynamic tenant-queue binding. QShare is readily implementable
with existing switching chips. We have implemented a QShare prototype and
evaluated it via both testbed experiments and simulations. Our results show
that QShare ensures bandwidth guarantees while driving network utilization to
over 91% even under unpredictable traffic demands.Comment: The initial work is published in IEEE INFOCOM 201
Maintaining flow isolation in work-conserving flow aggregation
Abstract — In order to improve the scalability of scheduling protocols with bounded end-to-end delay, much effort has focused on reducing the amount of per-flow state at routers. One technique to reduce this state is flow aggregation, in which multiple individual flows are aggregated into a single aggregate flow. In addition to reducing per-flow state, flow aggregation has the advantage of a per-hop delay that is inversely proportional to the rate of the aggregate flow, while in the case of no aggregation, the per-hop delay is inversely proportional to the (smaller) rate of the individual flow. Flow aggregation in general is non-work-conserving. Recently, a work-conserving flow aggregation technique has been proposed. However, it has the disadvantage that the end-to-end delay of an individual flow is related to the burstiness of other flows sharing its aggregate flow. Here, we show how work-conserving flow aggregation may be performed without this drawback, that is, the end-to-end delay of an individual flow is independent of the burstiness of other flows. I
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