Keqiang He Weite Qin Qiwei Zhang Wenfei Wu Junjie Yang Tian Pan Chengchen Hu Jiao Zhang Brent Stephens Aditya Akella Ying Zhang 1 Bandwidth Allocation in Clouds ID: 616879
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Low-Latency Software Rate Limiters for Cloud Networks
Keqiang He, Weite Qin, Qiwei Zhang, Wenfei Wu, Junjie Yang, Tian Pan, Chengchen Hu, Jiao Zhang, Brent Stephens, Aditya Akella, Ying Zhang
1Slide2
Bandwidth Allocation in Clouds
Provide performance isolationAllocate bandwidth for tenantsPrioritize applicationsImplemented by Software Rate LimitersConfigured on NICsE.g., Linux Hierarchical Token Buffer filter (HTB)2
10G server
VM1
VM2
VM3
RL1
RL2
RL3
4Gbps
4Gbps
2Gbps
RL: Rate LimiterSlide3
Software Rate Limiters
Maintain a queue to absorb packetsAssigned tokensDequeue packets according to tokensRefresh tokens periodically according to bandwidth allocation3Slide4
However, queuing delay is introduced
Motivating Experiment4
number of flows
Rate limitingSlide5
Software Rate Limiters introduce queuing latency
5TCP RTT is increased by 10X or even more
Goal: To build a low-latency software rate
limiterSlide6
Contents
Background & Problem StatementDesignEvaluationConclusion & Future Work6Slide7
Strawman Solution: Extending ECN into Rate Limiters
7VMDCTCP
Rate Limiter
Queues
Marking
Threshold
Extending ECN into Rate Limiters
: set ECN bits in IP header based on queue length
VM
DCTCP
VM
DCTCPSlide8
ECN+DCTCP: Lead to Throughput Oscillation
8Network Latency is reduced, but throughput oscillatesSlide9
Reasons of Oscillation
Control loop latencyOne RTTInflated by in-network latencyCoarse-grained ECN markingMarking segments, not packets64KB segment 43 packets (1500B)Aggressive CWND Computation
9Slide10
Direct ECE Marking (DEM)
10sender
receiver
Rate limiter queue
Outgoing data packets
Incoming TCP ACK
1. Control
loop latency
is almost ZERO
2.
F
ine-grained
congestion feedback Slide11
Further Improvement: get rid of ECN?
ECN may not be enabledTenant VM, Internet end hostsSolution: SPRINGReplay congestion control algorithm at rate limiterEnforce computed CWND to RWND field in ACK packets11Slide12
Contents
Background & Problem StatementDesignEvaluationConclusion & Future Work12Slide13
Performance of DEM
13Both low latency and high throughput are achieved using DEM
DEM works ECN-enabled flows onlySlide14
Performance of SPRING
14Both low latency and high throughput are achieved using SPRING
SPRING works
for both
ECN and non-ECN flowsSlide15
Conclusions
Software rate limiters introduce network latencyDCTCP+ECN causes throughput oscillationOne-RTT control loop latencySegment-level markingDirect ECE Markinghigh bandwidth saturation, low latency, low oscillationSPRING gets rid of ECNFuture workFairness, overhead, compatibility15Slide16
End
Thanks!Q&Awenfeiwu@tsinghua.edu.cn16