Optimizing UDP-based Protocol Implementations

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Optimizing UDP-based Protocol Implementations

• Yunhong Gu and Robert L. Grossman
• Presenter Michal Sabala

National Center for Data Mining
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Outline

• UDP Performance Characteristics and Optimizations
• Composable UDT A Framework for UDP-based
  Protocol Implementations

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Part I. UDP Performance Characteristics and
Optimization Techniques
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Introduction

• UDP-based Protocol is needed
• As short-term solution to the lack of effective
  kernel space transport protocols for high
  bandwidth-delay product networks
• As application specific data transfer library,
  e.g., Multimedia data transfer
• It is not an easy task to impalement a new
  UDP-based protocol from scratch
• And may be not necessary!

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UDP Performance

• Sending and receiving buffer size
• Packet size
• IO mode
• Scattering/gathering (writev/readv)
• Memory copy avoidance (e.g., overlapped IO of
  Windows Socket2)
• To reach same data transfer rate, UDP needs
  slightly less CPU time than TCP, and cause
  slightly less end system delay

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UDP Performance Impact of Buffer Size
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UDP Performance Impact of Packet Size
Throughput
CPU Util.
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UDP-based Protocol Performance

• Additional overhead
• Additional memory copy
• Additional packet processing
• Additional context switches

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Optimization Guidelines

• Avoid additional memory copy
• Reduce the number of packets
• Control packets, esp. acknowledgements
• Reduce overall processing time
• Simpler mechanism is better
• Avoid burst in processing time
• CPU may be too busy to process incoming packets

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Optimization Guidelines

• Memory copy avoidance
• UDP IO
• API semantics
• Acknowledgements
• Timer-based Acknowledging
• Light ACK
• Loss processing
• Timing, rate control, and self-clocking

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Optimization Guidelines

• Disk IO
• sendfile/recvfile
• Threading
• Synchronization cost
• Code Optimization
• sending/receiving loop
• Profiling

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Part II. Composable UDT A Framework for
UDP-based Protocol Implementations
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Composable UDT

• Based on the UDT (UDP-based Data Transfer
  library) implementation
• Integrated those optimization techniques
  described in this paper

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Objectives

• Rapid development of UDP-based transport
  protocols and application specific data transfer
  libraries
• Easy evaluation of new congestion control
  algorithms
• Non-objectives
• Replace kernel space protocol implementations
• User-level TCP implementation

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Current Status

• UDT/CCC Configurable congestion control
• In future
• Data reliability configuration
• Message boundary support

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Configurable Congestion Control

• Packet sending control
• Rate-based, window-based, hybrid
• Redefinition of control event handlers
• Loss, ACK, Time Out, etc.
• Access to internal protocol parameters
• RTT, RTO, Loss Rate, etc.
• User customized packet formats

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Implementation

• C class inheritance
• CCC base class for control event handing
• Callbacks
• Performance monitoring
• Internal protocol parameters
• Performance statistics

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Implementation
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Example Simplified TCP
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Configurable Congestion Control
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Future Work

• Continue to improve the UDT/CCC library
• More experimental evaluation work of the UDT/CCC
  library
• Compare k-TCP and u-TCP in more network
  environments
• Implement more TCP variants
• More pre-implemented congestion control algorithms

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Conclusion

• UDP-based protocol is one of the solutions to
  bulk data transfer in high BDP networks
• Some optimization principles and techniques are
  discussed in this paper
• We further propose a composable framework in
  order to make it much easier to implement
  UDP-based protocols

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Thank you!

• For more information, please visit
• UDT Project http//udt.sf.net
• NCDM http//www.ncdm.uic.edu

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Backup Slides
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UDP Performance Experiment Setup
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UDP Performance CPU Utilization
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UDP Performance End System Delay
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UDT Profiling Modules
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UDT Profiling Functionalities
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CPU Utilization K-TCP vs U-TCP