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Packet Order Matters!

Improving Application Performance by Deliberately Delaying Packets

Time: Tue 2021-06-01 17.00

Location: zoom link for online defense (English)

Subject area: Information and Communication Technology

Doctoral student: Hamid Ghasemirahni , Network Systems Laboratory (NS Lab)

Opponent: Professor Alan L. Davis, University of Utah, School of Computer Science

Supervisor: Professor Dejan Kostic, Kommunikationssystem, CoS

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Data-centers increasingly deploy commodity servers with high-speed network interfaces to enable low-latency communication. However, achieving low latency at high data rates crucially depends on how the incoming traffic interacts with the system's caches. When packets that need to be processed in the same way are consecutive, i.e., exhibit high temporal and spatial locality, CPU caches deliver great benefits.

This licentiate thesis systematically studies the impact of temporal and spatial traffic locality on the performance of commodity servers equipped with high-speed network interfaces. The results are that (i) the performance of a variety of widely deployed applications degrade substantially with even the slightest lack of traffic locality, and (ii) a traffic trace from our organization's link to/from its upstream provider reveals poor traffic locality as networking protocols, drivers, and the underlying switching/routing fabric spread packets out in time (reducing locality). 

To address these issues, we built Reframer, a software solution that deliberately delays packets and reorders them to increase traffic locality. Despite introducing µs-scale delays of some packets, Reframer increases the throughput of a network service chain by up to 84% and reduces the flow completion time of a web server by 11% while improving its throughput by 20%.