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Llnw bufferbloat
This document discusses the problem of bufferbloat on the internet. It explains that bufferbloat occurs when routers and switches have too much buffering capacity, which leads to increased latency. The causes of bufferbloat include increased bandwidth usage from applications, large TCP initial windows, and routers being configured to avoid dropping packets. Solutions presented are queue management techniques like CoDel and PIE that aim to control latency while maintaining high throughput. The document notes that while awareness of bufferbloat has increased, legacy equipment and congestion on backbones continue to cause issues.
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Llnw bufferbloat
- 1. BufferbloatBufferbloat Why is theInternet slow?Why is the Internet slow? Stephen HemmingerStephen Hemminger stephen@networkplumber.orgstephen@networkplumber.org Limelight Networks May 2015
- 3. BufferbloatBufferbloat ● What isthe problemWhat is the problem ● What causes the problemWhat causes the problem ● SolutionsSolutions – DemonstrationDemonstration ● Current statusCurrent status – The GoodThe Good – The BadThe Bad – The UglyThe Ugly
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- 5. How bad isit?How bad is it?
- 6. Why is worsenow?Why is worse now? ● No longer in FTP universeNo longer in FTP universe ● TCP Initial Window Size = 10TCP Initial Window Size = 10 ● Advanced TCP algorithmsAdvanced TCP algorithms ● Network Offload packet trainsNetwork Offload packet trains ● Bad benchmarksBad benchmarks ● Router/switch memory is cheapRouter/switch memory is cheap ● Everyone fears dropping packetsEveryone fears dropping packets
- 7. Head of LineblockingHead of Line blocking
- 8. Queuing Theory BasicsQueuingTheory Basics averagetimeinqueue utilization servicerate 1 utilization Graphic courtesy Sprint, Apricot 2004 From Fred Baker: Bufferbloat!
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- 12. TCP throughput dynamicsTCPthroughput dynamicsIncreasingMeasurableThroughput Increasing TCP Window “knee” “cliff” Bottleneck Capacity Queue Depth meanthroughput effectivewindow meanroundtriptime From Fred Baker: Bufferbloat!
- 13. Blame LinuxBlame Linux ●Windows XPWindows XP – Maximum window 64kMaximum window 64k ● Windows 7Windows 7 – Bandwidth limit to 80 mbitsBandwidth limit to 80 mbits ● AndroidAndroid – Receive window limitedReceive window limited
- 14. Blame the customerBlamethe customer ● Customers callCustomers call supportsupport ● Applications areApplications are using moreusing more bandwidthbandwidth ● Block and chargeBlock and charge
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- 17. Priority Queue: TheoryPriorityQueue: Theory
- 18. Priority Queue: RealityPriorityQueue: Reality
- 19. Hierarchical Token BucketHierarchicalToken Bucket
- 20. Random Early DetectRandomEarly Detect
- 21. Explicit Congestion NotificationExplicitCongestion Notification PACKETS
- 22. Ideal Active QueueManagementIdeal Active Queue Management ● FairFair – All flows get some bandwidthAll flows get some bandwidth ● SimpleSimple – No tuningNo tuning ● Easy to deployEasy to deploy – No special hardware, no protocol changesNo special hardware, no protocol changes ● ReasonableReasonable – Won't create multi-second latencyWon't create multi-second latency
- 23. Stocastic Fair QueueStocasticFair Queue
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- 28. Benchmark issuesBenchmark issues ●BadBad – Bytes/secBytes/sec – Packes/secPackes/sec – LatencyLatency ● GoodGood – Throughput + LatencyThroughput + Latency – Multiple connectionsMultiple connections – Real not simulatedReal not simulated
- 29. Better toolsBetter tools ●DSLreport'sDSLreport's – http://www.dslreports.com/speedtest/http://www.dslreports.com/speedtest/ ● ICSI netalyzrICSI netalyzr – http://netalyzr.icsi.berkeley.edu/http://netalyzr.icsi.berkeley.edu/ ● Real time Response Under LoadReal time Response Under Load – https://github.com/tohojo/netperf-wrapperhttps://github.com/tohojo/netperf-wrapper – Flent: The Flexible Network TesterFlent: The Flexible Network Tester
- 30. DSLReports speedtestDSLReports speedtest 5sec delay!!
- 31. FIFO – thedefaultFIFO – the default Høiland-Jørgensen T., Battling Bufferbloat Ping 1sec! Upload Download
- 32. Stochastic Fair QueueStochasticFair Queue Høiland-Jørgensen T., Battling Bufferbloat
- 33. Controlled Delay -codelControlled Delay - codel Høiland-Jørgensen T., Battling Bufferbloat
- 34. Fair Queue ControlledDelayFair Queue Controlled Delay Høiland-Jørgensen T., Battling Bufferbloat
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- 36. Bufferbloat: The GoodBufferbloat:The Good ● Industry awarenessIndustry awareness ● Standards progressStandards progress ● Active researchActive research ● Open Source SolutionsOpen Source Solutions
- 37. Once you startlooking,Once you start looking, Bufferbloat can be everywhereBufferbloat can be everywhere ● EdgeEdge – Home routerHome router ● ProviderProvider ● NetworkNetwork ● AcceleratorsAccelerators – CachesCaches – Load balancers,...Load balancers,... ● ServersServers
- 38. How is BufferbloatSolved on Linux?How is Bufferbloat Solved on Linux? ● Queuing disciplinesQueuing disciplines – Codel, PIE, ...Codel, PIE, ... ● Linux internalLinux internal – BQL, FQ, PacingBQL, FQ, Pacing ● Enable good defaultsEnable good defaults – ecnecn – fq_codelfq_codel
- 39. Bufferbloat: the BadBufferbloat:the Bad ● Legacy equipmentLegacy equipment – OEM focus on cost not AQMOEM focus on cost not AQM ● Congestion on backboneCongestion on backbone – It's not a bug it's a feature?It's not a bug it's a feature? – Problem is political not technicalProblem is political not technical
- 40. Bufferbloat: the UglyBufferbloat:the Ugly ● WirelessWireless – AggregationAggregation – MulticastMulticast – Bad benchmarksBad benchmarks – Proprietary firmwareProprietary firmware
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- 43. Bufferbloat resources Bufferbloat.net: http://bufferbloat.net EmailLists: http://lists.bufferbloat.net CeroWrt: http://www.bufferbloat.net/projects/cerowrt Other talks: http://mirrors.bufferbloat.net/Talks Jim Gettys Blog – http://gettys.wordpress.com A big thanks to the bloat mailing list, Jim, Kathie, Van, Dave, Eric, ISC, and all the other the CeroWrt/OpenWrt contributors
Editor's Notes
- #5 Bufferbloat has been known about in the academic community but was not generally measured because many tests only measured one dimension
- #6 150ms – VOIP 20ms – Desktop lag 100ms – DNS lookup fail ARP, ND – Can't find machine .5sec – User's give up 2 sec–scp copy fails DHCP – Machine falls off network
- #8 Bufferbloat: The sometimes extreme delays in the Internet caused by excess queuing.
- #9 As the utilization goes to 100% the delay goes to infinity. Green = T1 Blue = 10Mbit
- #13 <number> Effective Window: the amount of data TCP sends each RTT Knee: the lowest window that makes throughput approximate capacity Cliff: the largest window that makes throughput approximate capacity Note that throughput is the same at knee and cliff. Increasing the window merely increases RTT, by increasing queue depth
- #15 Split or use transistions?