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Chair for Network Architectures and Services Technical University of Munich Component Model for Linux-based Network Systems Guided Research Dominik Scholz March 16, 2016 Chair for Network Architectures and Services Department of Informatics

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Chair for Network Architectures and Services Technical University of Munich

Component Model for Linux-based Network Systems

Guided Research Dominik Scholz

March 16, 2016 Chair for Network Architectures and Services Department of Informatics Technical University of Munich

Dominik Scholz – Component Model for Linux-based Network Systems 1

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Chair for Network Architectures and Services Technical University of Munich

Motivation

Profiling of Linux Network Stack Research Questions

Linux Network Stack

Routing Subsystem Netfilter

Component Model

Methodology

Evaluation

IPv4 & IPv6 Forwarding Performance NAT

Conclusion

iptables

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Chair for Network Architectures and Services Technical University of Munich

Motivation Software routers are faced with new challenges

◮ Standards beyond 10 GbE: 40 GbE and 100 GbE [1] ◮ Growing routing tables: >550.000 rules for backbone

routers [2]

◮ Deployment of IPv6 ◮ Multifaceted tasks (packet filter, NAT, ...)

How can performance be analysed?

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Chair for Network Architectures and Services Technical University of Munich

Profiling of Linux Network Stack Network Stack

◮ Full data plane functionality ◮ Customisable

Profiling using perf

◮ SW/HW counters (e.g. CPU cycles, cache misses) ◮ Use to understand processing and find potential

bottlenecks

◮ Problem: hundreds of functions

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Chair for Network Architectures and Services Technical University of Munich

Visualised Call-Stack

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Chair for Network Architectures and Services Technical University of Munich

Research Questions

◮ How can profiling be used to analyse the performance of

routers?

◮ How is the performance of IPv4 and IPv6 software routers? ◮ Can optional/additional tasks (packet filter, NAT, ...) be

analysed with this method?

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Chair for Network Architectures and Services Technical University of Munich

Linux Network Stack – Forwarding

NIC NIC ip rcv ip forward ip output NF Hooks PRE FWD POST Routing Subsystem conntrack iptable filter nat ipv4 out

IPv6: similar but separate path

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Chair for Network Architectures and Services Technical University of Munich

Components – Routing Subsystem Where to forward packet to? → Longest Prefix Matching Data Structure: FIB trie [3]

◮ Ordered prefix tree, IP used as key ◮ Lookup has O(n) complexity, n is length of key [4]

→ n is known → Independent of number of entries!

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Chair for Network Architectures and Services Technical University of Munich

Components – Netfilter Several hooks during processing path of packet → Forwarding: prerouting, forwarding, postrouting hooks Source NAT

◮ Connection tracking (prerouting) ◮ Packet modifications (postrouting)

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Chair for Network Architectures and Services Technical University of Munich

Component Model

Cr Cprer Cpostr Cct Cipt Cnat out Cnet

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Chair for Network Architectures and Services Technical University of Munich

Methodology Data generation

◮ Generate load (MoonGen) ◮ Measure RX and TX packet rate of router ◮ Profiling with perf

◮ Percentage distribution of CPU cycles across functions ◮ Total CPU cycles ◮ L1, L2, LLC cache misses

Data processing

◮ Calculate cycles per function per packet ◮ Sort into groups (based on call-stack, source code)

Problem: functions reused during different steps of processing

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Chair for Network Architectures and Services Technical University of Munich

Forwarding Performance – Parameterized Model

Cprer Cct Cr Cipt Cpostr Cnat_out

100 200 300 400 500 600 700 800 900

CPU-cycles per packet 1 flow 2 flows 64 flows 256 flows 1k flows 16k flows 100k flows 500k flows 1mil flows

(a) IPv4

Cprer Cct Cr Cipt Cpostr Cnat_out

500 1000 1500 2000 2500

CPU-cycles per packet 1 flow 2 flows 64 flows 256 flows 1k flows 16k flows 500k flows 1mil flows

(b) IPv6

→ Only routing subsystem influences performance

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Chair for Network Architectures and Services Technical University of Munich

Forwarding Performance

100 101 102 103 104 105 106 2,000 2,500 3,000 3,500 Flows [log] Cycles per Packet [-] 100 101 102 103 104 105 106 5 10 15 20 Cache Misses per Packet [-] Cycles L1 cache misses L2 cache misses L3 cache misses

(a) IPv4

(b) IPv6

→ Areas of approx. constant cost because of FIB trie

◮ Constant lookup cost ◮ Linear in regard to memory → cache sizes!

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Chair for Network Architectures and Services Technical University of Munich

NAT – IPv4

Cprer Cct Cr Cipt Cpostr Cnat_out

500 1000 1500 2000

CPU-cycles per packet 1 flow 1k flows 16k flows 32k flows

(a) Profiling

100 101 102 103 104 4,000 4,500 5,000 5,500 6,000 6,500 7,000 Flows [log] Cycles per Packet [-] 100 101 102 103 104 5 10 15 20 25 30 Cache Misses per Packet [-] Cycles L1 cache misses L2 cache misses L3 cache misses

(b) Performance

→ approx. constant cost of 1900 cpp for up to 10000 rules

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Chair for Network Architectures and Services Technical University of Munich

Conclusion Methodology

◮ Difficult for complex scenarios, functions reused!

→ alternative approach: once with frame-pointers (performance loss!) to calibrate model

◮ Can be applied to other software routers

→ e.g. analyse different forwarding algorithms Forwarding with Linux Network Stack

◮ IPv6 significantly slower: longer addresses → caching ◮ ... but for instance no need for NAT

Paper submitted to ITC

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Chair for Network Architectures and Services Technical University of Munich

Bibliography I

[1] D. J. Law, A. Healey, P . Anslow, S. B. Carlson, and V. Maguire: IEEE 802.3bm-2015 (2015). [2] Huston, G.: BGP in 2015. In: labs.apnic.net (2016) [3] LC-trie implementation notes. Available: www.kernel.org/doc/Documentation/networking/fib_trie.txt [4] Bellini, A.C.: The Trie: A Neglected Data Structure. Available: www.toptal.com/java/the-trie-a-neglected-data-structure

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Chair for Network Architectures and Services Technical University of Munich

Thank you for your attention!

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Chair for Network Architectures and Services Technical University of Munich

iptables – IPv4, stateless

Cprer Cct Cr Cipt Cpostr Cnat_out

500 1000 1500 2000

CPU-cycles per packet 2 rules 32 rules 64 rules 128 rules

(a) Profiling

100 101 102 103 104 101 102 103 104 105 Stateless Rules [log] Cycles per Packet [log] 100 101 102 103 104 100 101 102 103 Cache Misses per Packet [log] Cycles L1 cache misses L2 cache misses

(b) Performance

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