An experimental study of the learnability of congestion control

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1 An experimental study of the learnability of congestion control Anirudh Sivaraman, Keith Winstein, Pratiksha Thaker, Hari Balakrishnan MIT CSAIL August 31, / 17

2 This talk How easy is it to learn a network protocol to achieve a desired goal, despite a mismatched set of assumptions? 2 / 17

3 This talk How easy is it to learn a network protocol to achieve a desired goal, despite a mismatched set of assumptions? cf. Learning: Knowledge acquisition without explicit programming (Valiant 1984) 2 / 17

4 Preview of key results 3 / 17

5 Preview of key results Can tolerate mismatched link-rate assumptions 3 / 17

6 Preview of key results Can tolerate mismatched link-rate assumptions Need precision about the number of senders 3 / 17

7 Preview of key results Can tolerate mismatched link-rate assumptions Need precision about the number of senders TCP compatibility is a double-edged sword 3 / 17

8 Preview of key results Can tolerate mismatched link-rate assumptions Need precision about the number of senders TCP compatibility is a double-edged sword Can tolerate mismatch in the # of bottlenecks 3 / 17

9 Experimental method 4 / 17

10 Experimental method 4 / 17

11 Experimental method < Mbps, ms> 4 / 17

12 Experimental method < Mbps, ms> 4 / 17

13 Experimental method < Mbps, ms> 4 / 17

14 Experimental method < Mbps, ms> 4 / 17

15 Experimental method < Mbps, ms> 4 / 17

16 Experimental method Training Networks < Mbps, ms> 5 / 17

17 Experimental method Training Networks Objective Function: - log (tpt/delay) - Avg. Flow Completion time < Mbps, ms> Learner 5 / 17

18 Experimental method Training Networks Objective Function: - log (tpt/delay) - Avg. Flow Completion time < Mbps, ms> Learner Congestion Control Algorithm 5 / 17

19 Experimental method Training Networks Objective Function: - log (tpt/delay) - Avg. Flow Completion time < Mbps, ms> Remy (SIGCOMM 13) RemyCC 5 / 17

20 Experimental method Training Networks Objective Function: - log (tpt/delay) - Avg. Flow Completion time Testing Networks < Mbps, ms> < Mbps, ms> Remy (SIGCOMM 13) RemyCC Test within ns-2 5 / 17

21 Remy compared with an ideal protocol Throughput (Mbps) Queueing delay (ms) 6 / 17

22 Remy compared with an ideal protocol 32 Ideal 16 Throughput (Mbps) Queueing delay (ms) 6 / 17

23 Remy compared with an ideal protocol Ideal RemyCC Throughput (Mbps) Queueing delay (ms) 6 / 17

24 Remy compared with an ideal protocol 32 Ideal 16 RemyCC Throughput (Mbps) Cubic Cubic/sfqCoDel Queueing delay (ms) 6 / 17

25 Learning network protocols despite mismatched assumptions 7 / 17

26 Learning network protocols despite mismatched assumptions Is there a tradeoff between operating range and generality in link rates? 7 / 17

27 Learning network protocols despite mismatched assumptions Is there a tradeoff between operating range and generality in link rates? Is there a tradeoff between performance and operating range in link rates? 7 / 17

28 Performance and link-rate operating range Objective Function (Normalized) Link rate (Mbps) 8 / 17

29 Performance and link-rate operating range 0 Ideal -0.5 Objective Function (Normalized) Link rate (Mbps) 8 / 17

30 Performance and link-rate operating range 2x range 0 Ideal -0.5 Objective Function (Normalized) Link rate (Mbps) 8 / 17

31 Performance and link-rate operating range 2x range 10x range 0 Ideal -0.5 Objective Function (Normalized) Link rate (Mbps) 8 / 17

32 Performance and link-rate operating range 0 2x range 10x range 100x range Ideal -0.5 Objective Function (Normalized) Link rate (Mbps) 8 / 17

33 Performance and link-rate operating range 0 2x range 10x range 100x range 1000x range Ideal -0.5 Objective Function (Normalized) Link rate (Mbps) 8 / 17

34 Performance and link-rate operating range 0 2x range 10x range 100x range 1000x range Ideal -0.5 Objective Function (Normalized) -1 Cubic-over-sfqCoDel -1.5 Cubic Link rate (Mbps) 8 / 17

35 Performance and link-rate operating range 9 / 17

36 Performance and link-rate operating range Very clear generality vs. operating range tradeoff 9 / 17

37 Performance and link-rate operating range Very clear generality vs. operating range tradeoff Only weak evidence of a performance vs. operating range tradeoff 9 / 17

38 Performance and link-rate operating range Very clear generality vs. operating range tradeoff Only weak evidence of a performance vs. operating range tradeoff Possible to design a forwards-comptabible protocol handling a wide range in link rates 9 / 17

39 Learning network protocols despite mismatched assumptions Can we learn a protocol that performs well both when there are few senders and when there are many senders? 10 / 17

40 Imperfections in the number of senders Normalized objective function Number of senders 11 / 17

41 Imperfections in the number of senders 0.0 Ideal 0.2 Normalized objective function Number of senders 11 / 17

42 Imperfections in the number of senders 0.0 Ideal 0.2 Normalized objective function Number of senders 11 / 17

43 Imperfections in the number of senders 0.0 Ideal 0.2 Normalized objective function Number of senders 11 / 17

44 Imperfections in the number of senders 0.0 Ideal 0.2 Normalized objective function Number of senders 11 / 17

45 Imperfections in the number of senders 0.0 Ideal 0.2 Normalized objective function Number of senders 11 / 17

46 Imperfections in the number of senders 0.0 Ideal 0.2 Normalized objective function Number of senders 11 / 17

47 Imperfections in the number of senders 0.0 Ideal Normalized objective function Number of senders 11 / 17

48 Imperfections in the number of senders 0.0 Ideal Normalized objective function Number of senders 11 / 17

49 Imperfections in the number of senders 0.0 Ideal Normalized objective function Number of senders 11 / 17

50 Imperfections in the number of senders 0.0 Ideal Normalized objective function Number of senders 11 / 17

51 Imperfections in the number of senders 0.0 Ideal Normalized objective function Cubic Number of senders 11 / 17

52 Imperfections in the number of senders 0.0 Ideal Normalized objective function Cubic Cubic-over-sfqCoDel Number of senders 11 / 17

53 Imperfections in the number of senders Tradeoff between performance with few senders and performance with many senders 11 / 17

54 Learning network protocols despite mismatched assumptions What are the costs and benefits of learning a new protocol that shares fairly with a legacy sender? 12 / 17

55 Imperfect assumptions about the nature of other senders TCP-Aware RemyCC: Contends with: TCP-Aware RemyCC half the time TCP NewReno half the time. 13 / 17

56 Imperfect assumptions about the nature of other senders TCP-Aware RemyCC: Contends with: TCP-Aware RemyCC half the time TCP NewReno half the time. TCP-Naive RemyCC: Contends with: TCP-Naive RemyCC all the time 13 / 17

57 RemyCC competing against itself 7 6 Throughput (Mbps) 5 NewReno RemyCC [TCP-naive] 4 Better Queueing delay (ms) 14 / 17

58 RemyCC competing against itself 7 6 Throughput (Mbps) 5 NewReno RemyCC [TCP-naive] Cost of TCP-awareness 4 Better Queueing delay (ms) 14 / 17

59 RemyCC competing against itself 7 6 Throughput (Mbps) 5 NewReno RemyCC [TCP-aware] RemyCC [TCP-naive] Cost of TCP-awareness 4 Better Queueing delay (ms) 14 / 17

60 RemyCC competing against TCP NewReno 7 NewReno 6 Throughput (Mbps) 5 4 RemyCC [TCP-naive] Better Queueing delay (ms) / 17

61 RemyCC competing against TCP NewReno 7 NewReno 6 Throughput (Mbps) 5 Effect of TCP-aware adversary 4 RemyCC [TCP-naive] Benefit of TCP-awareness Better Queueing delay (ms) 15 / 17

62 RemyCC competing against TCP NewReno 7 NewReno 6 Throughput (Mbps) 5 Effect of TCP-aware adversary NewReno RemyCC [TCP-aware] 4 RemyCC [TCP-naive] Benefit of TCP-awareness Better Queueing delay (ms) 15 / 17

63 RemyCC competing against TCP NewReno TCP awareness benefits you when needed, costs if you don t 15 / 17

64 Caveats 16 / 17

65 Caveats Remy as a proxy for an optimal learner 16 / 17

66 Caveats Remy as a proxy for an optimal learner Results may change with better learners 16 / 17

67 Caveats Remy as a proxy for an optimal learner Results may change with better learners Negative results may no longer hold 16 / 17

68 The learnability of congestion control 17 / 17

69 The learnability of congestion control Can tolerate mismatched link-rate assumptions 17 / 17

70 The learnability of congestion control Can tolerate mismatched link-rate assumptions Need precision about the number of senders 17 / 17

71 The learnability of congestion control Can tolerate mismatched link-rate assumptions Need precision about the number of senders TCP compatibility is a double-edged sword 17 / 17

72 The learnability of congestion control Can tolerate mismatched link-rate assumptions Need precision about the number of senders TCP compatibility is a double-edged sword Can tolerate mismatch in the # of bottlenecks 17 / 17

73 The learnability of congestion control Can tolerate mismatched link-rate assumptions Need precision about the number of senders TCP compatibility is a double-edged sword Can tolerate mismatch in the # of bottlenecks Ongoing work in using findings: 17 / 17

74 The learnability of congestion control Can tolerate mismatched link-rate assumptions Need precision about the number of senders TCP compatibility is a double-edged sword Can tolerate mismatch in the # of bottlenecks Ongoing work in using findings: improve Google s datacenter transport 17 / 17

75 The learnability of congestion control Can tolerate mismatched link-rate assumptions Need precision about the number of senders TCP compatibility is a double-edged sword Can tolerate mismatch in the # of bottlenecks Ongoing work in using findings: improve Google s datacenter transport user-space implementation of RemyCC 17 / 17

76 The learnability of congestion control Can tolerate mismatched link-rate assumptions Need precision about the number of senders TCP compatibility is a double-edged sword Can tolerate mismatch in the # of bottlenecks Ongoing work in using findings: improve Google s datacenter transport user-space implementation of RemyCC 17 / 17

77 Backup slides 17 / 17

78 The Remy protocol synthesis procedure Protocol: range-based rule table from state to action 17 / 17

79 The Remy protocol synthesis procedure Protocol: range-based rule table from state to action State: Congestion signals tracked by the sender s ewma : EWMA over packet inter-transmit times r ewma : EWMA over ACK inter-arrival times rtt ratio: Ratio of RTT to minimum RTT slow r ewma: Slower version of s ewma 17 / 17

80 The Remy protocol synthesis procedure Protocol: range-based rule table from state to action State: Congestion signals tracked by the sender s ewma : EWMA over packet inter-transmit times r ewma : EWMA over ACK inter-arrival times rtt ratio: Ratio of RTT to minimum RTT slow r ewma: Slower version of s ewma Action: modify window, transmission rate Multiplier m to current window Increment c to current window Minimum inter-transmit time. 17 / 17

81 The Remy protocol synthesis procedure 1. Start with one rule: one action for all states 2. Optimize each action to maximize objective 3. Find most used rule 4. Median split that rule based on state usage 5. Repeat 2, 3, and 4 till you converge 17 / 17

82 One action for all states. Find the best value. r_ewma <?,?,?> s_ewma 17 / 17

83 The best (single) action. Now split it on median. r_ewma <0.90,4,3.3> s_ewma 17 / 17

84 Simulate <0.90,4,3.3> <0.90,4,3.3> r_ewma <0.90,4,3.3> <0.90,4,3.3> s_ewma 17 / 17

85 Optimize each of the new actions <0.90,4,3.3> <0.90,4,3.3> r_ewma <0.90,4,3.3> <0.90,4,3.3> s_ewma 17 / 17

86 Now split the most-used rule <0.90,5,2.8> <0.70,6,53.5> r_ewma <0.60,19,76.2> <0.80,5,4.1> s_ewma 17 / 17

87 Simulate <0.90,5,2.8> <0.70,6,53.5> r_ewma <0.80,5,4.1> <0.80,5,4.1> <0.60,19,76.2> <0.80,5,4.1> <0.80,5,4.1> s_ewma 17 / 17

88 Optimize <0.90,5,2.8> <0.70,6,53.5> r_ewma <0.80,5,4.1> <0.80,5,4.1> <0.60,19,76.2> <0.80,5,4.1> <0.80,5,4.1> s_ewma 17 / 17

89 Split <0.90,5,2.8> <0.60,17,13.3> r_ewma <0.80,8,3.3> <0.80,17,4.6> <0.30,29,49.7> <0.80,8,62.7> <0.80,7,16.9> s_ewma 17 / 17

90 Simulate <0.90,5,2.8> <0.90,5,2.8> <0.60,17,13.3> r_ewma <0.90,5,2.8> <0.90,5,2.8> <0.80,8,3.3> <0.80,17,4.6> <0.30,29,49.7> <0.80,8,62.7> <0.80,7,16.9> s_ewma 17 / 17

91 Can applications with different objectives coexist? Tpt. Sender: A throughput-intensive sender log(throughput) 0.1 log(delay) (1) Lat. Sender: A latency-sensitive sender log(throughput) 10.0 log(delay) (2) Running over a FIFO queue 17 / 17

92 Training for diversity has a cost Throughput (Mbps) Queueing delay (ms) 17 / 17

93 Training for diversity has a cost Throughput (Mbps) 5 Tpt. Sender [naive] Lat. Sender [naive] Queueing delay (ms) 17 / 17

94 Training for diversity has a cost Throughput (Mbps) Cost of Coexistence Tpt. Sender [naive] Tpt. Sender [coevolved] Lat. Sender [naive] Lat. Sender [coevolved] Queueing delay (ms) 17 / 17

95 but, benefits the docile sender Throughput (Mbps) Queueing delay (ms) 17 / 17

96 but, benefits the docile sender Tpt. Sender [naive] Throughput (Mbps) 5 2 Lat. Sender [naive] Queueing delay (ms) 17 / 17

97 but, benefits the docile sender 16 Throughput (Mbps) Tpt. Sender [naive] Effect of playing nice Lat. Sender [naive] Benefit of coevolution Tpt. Sender [coevolved] Lat. Sender [coevolved] Queueing delay (ms) 17 / 17

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