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Priority Based Forced Requeue to Reduce Worst-Case Latencies for Bursty Traffic
KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
2009 (English)In: DATE: 2009 DESIGN, AUTOMATION & TEST IN EUROPE CONFERENCE & EXHIBITION, 2009, 1070-1075 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper we introduce Priority Based Forced Requeue to decrease worst-case latencies in NoCs offering best effort services. Forced Requeue is to prematurely lift out low priority packets from the network and requeue them outside using priority queues. The first benefit of this approach, applicable to any NoC offering best effort services, is that packets that have not yet entered the network now compete with packets inside the network and hence tighter bounds on admission times can be given. The second benefit - which is more specific to deflective routing as in the Nostrum NoC - is that packet "reshuffling" dramatically reduces the latency inside the network for bursty traffic due to a lowered risk of collisions at the exit of the network. This paper studies the Forced Requeuing on a mesh with varying burst sizes and traffic scenarios. The experimental results show a 50% reduction in worst-case latency from a system perspective thanks to a reshaped latency distribution whilst keeping the average latency the same.

Place, publisher, year, edition, pages
2009. 1070-1075 p.
Series
Design, Automation and Test in Europe Conference and Expo, ISSN 1530-1591
Keyword [en]
Best effort services, Burst size, Bursty traffic, Low priorities, Priority queues, Priority-based, Risk perception
National Category
Computer and Information Science
Identifiers
URN: urn:nbn:se:kth:diva-30353ISI: 000273246700191Scopus ID: 2-s2.0-70350070728ISBN: 978-1-4244-3781-8 (print)OAI: oai:DiVA.org:kth-30353DiVA: diva2:401549
Conference
Design, Automation and Test in Europe Conference and Exhibition, Nice, FRANCE, APR 20-24, 2009
Note
QC 20110303Available from: 2011-03-03 Created: 2011-02-24 Last updated: 2011-11-24Bibliographically approved
In thesis
1. Architectural Techniques for Improving Performance in Networks on Chip
Open this publication in new window or tab >>Architectural Techniques for Improving Performance in Networks on Chip
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main aim of this thesis is to propose enhancing techniques for the performance in Networks on Chips. In addition, a concrete proposal for a protocol stack within our NoC platform Nostrum is presented. Nostrum inherently supports both Best Effort as well as Guaranteed Throughput traffic delivery. It employs a deflective routing scheme for best effort traffic delivery that gives a small footprint of the switches in combination with robustness to disturbances in the network. For the traffic delivery with hard guarantees a TDMA based scheme is used. During the transmission process in a NoC several stages are involved. In the papers included, I propose a set of strategies to enhance the performance in several of these stages. The strategies are summarised as follows

Temporally Disjoint Networks is that a physical network, potentially, can be seen to contain a set of separate networks that a packet can enter dependenton when it enters the physical network. This has the consequence that wecould have different traffic types in the different networks.

Looped containers provide means to set up virtual circuits in networksusing deflective routing. High priority container packets are inserted intothe network to follow a predefined, closed, route between source and destination.At sender side the packets are loaded and sent to the destination where it is unloaded and sent back.

Proximity Congestion Awareness reduces the load of the network by diverting packets away from congested areas. It can increase the maximum trafficload by a factor of 20.

Dual Packet Exit increases the exit bandwidth of the network leading to a50 percent reduction in worst-case latency and a 30 percent reduction inaverage latency as well as a lowered buffer usage.

Priority Based Forced Requeue prematurely lifts out low priority packetsfrom the network to be requeued. Packets that have not yet entered the network compete with packets inside the network which gives tighter boundson admission with a reduction of worst case latencies by 50 percent.

Furthermore, Operational Efficiency is proposed as a measure to quantifyhow effective a network is and is defined as the throughput per buffers used in the system. An increase of the injection of packets into the network to increase the system throughput will have a cost associated to it and can be optimised to save energy.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xxiv, 103 p.
Series
Trita-ICT-ECS AVH, ISSN 1653-6363 ; 11:13
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-48243 (URN)978-91-7501-169-1 (ISBN)
Public defence
2011-12-08, Sal D, KTH-Forum, Isafjordsgatan 39, Kista, 13:00 (English)
Opponent
Supervisors
Note
QC 20111124Available from: 2011-11-24 Created: 2011-11-16 Last updated: 2012-01-16Bibliographically approved

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