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LiNK: An Operating System Architecture for Network Processors

LiNK: An Operating System Architecture for Network Processors. Steve Muir , Jonathan Smith Princeton University, University of Pennsylvania (smuir@cs.princeton.edu, jms@cis.upenn.edu). The Network Processor environment. Many types of network device include a processor

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LiNK: An Operating System Architecture for Network Processors

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  1. LiNK: An Operating System Architecture for Network Processors Steve Muir , Jonathan Smith Princeton University, University of Pennsylvania (smuir@cs.princeton.edu, jms@cis.upenn.edu)

  2. The Network Processor environment • Many types of network device include a processor • High performance host NICs e.g., gigabit cards • Remote management (ILO) devices • Router line cards • Virtual network devices (more on this later...)

  3. Example applications • High-speed packet processing • Traffic shaping • Firewall/intrusion detection • Monitoring/logging • Remote management

  4. Why a network processor OS? • Device-independent portability layer • run the same application on diverse network processors • Hardware abstraction • hide details of network processor environment from app. • Isolation between components • protect services and drives from bugs • Multitasking • simplifies the programming task • Library of common functionality • memory management, profiling, logging, etc.

  5. LiNK: The Lightweight Network Kernel • Simple, event-driven main loop • interrupt handlers scheduled as events • synchronous processing reduces complexity of kernel • Network service components • take advantage of simple, uniform application structure • Posted service requests • efficient communication between LiNK and clients

  6. Network Service Components • Fundamental structure shared by all applications • Three elements: 1. Transmit filter – add packet headers, packet scheduling 2. Receive handler – generate response packets 3. Timeout callback – flush caches, packet retransmit • Service functions scheduled by kernel • functions run to completion or explicit yield • Many services fit into this model • ARP, ICMP, traffic shaping

  7. Posted Service Request object

  8. Make_Frameset Alloc_Mem Alloc_Mem Set_Peer Cap_Ref_New Cap_Ref_New <Reference> Cap_Ref_New 12 192.168.0.1 12 Posted Service Request processing • Client posts to shared object - asynchrony • Kernel polls and processes - concurrency • Chaining required for efficiency • Speculation and reference arguments • Events for completion and failure notification Speculation <Reference> <Reference> Data Dependency

  9. Virtual Network Processors • Multi-core processors are cheaply available • multi-threaded and/or multi-core CPUs • Virtualisation technology has matured too • low overhead, enhanced by hardware support • Use a processing element as a network processor • A perfect prototyping and development environment • testing and debugging on real hardware is hard • But maybe something more...

  10. Current Implementation • Hybrid Linux/LiNK system • Linux as host operating system, LiNK as kernel module • LiNK accessible to Linux as standard ethernet device • LiNK provides user-space network subsystem • Linux provides filesystem, processes, scheduling, VM, etc. • Simple way to prototype new NP feature • e.g., a direct user-space interface to the (virtual) NP

  11. Evaluating the Virtual NIC • Ported the Flash webserver to Linux+LiNK • Provided TCP/IP protocol stack as user-space library • webserver used unmodified • WebStone 2.5 HTTP benchmark • simulates realistic workload with multiple clients • small number of files, representative size and distribution • Compare performance of Linux and Linux+LiNK

  12. Evaluation: Communication Overhead

  13. Evaluation: Flash performance

  14. Conclusions • Network processors need operating systems • The Lightweight Network Kernel is one alternative • Simple, specialised structure • Asynchronous, high performance communication • The future: virtual network processors

  15. Questions/comments

  16. Evaluation: Network Throughput

  17. Evaluation: Polling Performance

  18. Evaluation: Polling Scalability

  19. Related Work • Network device polling • Click modular router [Kohler] - 4x performance increase • Scout/IXP1200 router [Peterson] - similar • Parallel network protocol stacks [Bjornberg, Naburn] • processor-per-packet scales well for simple protocols • complex protocols => severe lock contention • Network appliance optimisations • I/O Lite - unified buffer management [Pai] • Soft timers - polling in an interrupt-driver kernel [Aron]

  20. Future Work • Responsiveness of polling • dynamic specialisation e.g., run-time code generation • Scalability • how many processors can Piglet support? • how many applications/devices? • Alternative applications for Piglet • network processor e.g., IXP1200, operating system

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