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The Only Constant is Change: Incorporating Time-Varying Bandwidth

Reservations in Data Centers

Di Xie, Ning Ding, Y. Charlie Hu, Ramana Kompella

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Cloud Computing is Hot

Private Cluster

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Key Factors for Cloud Viability

• Cost

• Performance

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Performance Variability in Cloud

• BW variation in cloud due to contention [Schad’10 VLDB]

• Causing unpredictable performance

Local Cluster Amazon EC20

100

200

300

400

500

600

700

800

900

1000

Bandwidth (Mbps)

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Reserving BW in Data Centers

• SecondNet [Guo’10]– Per VM-pair, per VM access bandwidth reservation

• Oktopus [Ballani’11]– Virtual Cluster (VC)– Virtual Oversubscribed Cluster (VOC)

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How BW Reservation Works

. . .

Virtual Cluster Model

Time

Bandwidth

N VMs

VirtualSwitch

1. Determine the model 2. Allocate and enforce the model

0 T

B

Only fixed-BW reservationRequest <N, B>

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Network Usage for MapReduce Jobs

Hadoop Sort, 4GB per VM

Hadoop Word Count, 2GB per VM

Hive Join, 6GB per VM

Hive Aggregation, 2GB per VM

Time-varying network usage

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Motivating Example

• 4 machines, 2 VMs/machine, non-oversubscribednetwork

• Hadoop Sort– N: 4 VMs– B: 500Mbps/VM

1Gbps

500Mbps500Mbps

500Mbps

Not enough BW

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Motivating Example

• 4 machines, 2 VMs/machine, non-oversubscribednetwork

• Hadoop Sort– N: 4 VMs– B: 500Mbps/VM

1Gbps

500Mbps

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Under Fixed-BW Reservation Model

1Gbps

500MbpsJob3Job2

Virtual Cluster Model

Job1 Time

0 5 10 15 20 25 30

500

Bandwidth

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Under Time-Varying Reservation Model

1Gbps

500Mbps

TIVC Model

Job1 Time

0 5 10 15 20 25 30

500Job2Job3Job4Job5

J1 J2J3 J4J5

Bandwidth

Doubling VM, network utilization and the job

throughput

HadoopSort

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Temporally-Interleaved Virtual Cluster (TIVC)

• Key idea: Time-Varying BW Reservations

• Compared to fixed-BW reservation– Improves utilization of data center

• Better network utilization• Better VM utilization

– Increases cloud provider’s revenue– Reduces cloud user’s cost– Without sacrificing job performance

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Challenges in Realizing TIVC

. . .

Virtual Cluster Model

Time

Bandwidth

N VMs

VirtualSwitch 0 T

B

Request <N, B>

Time

Bandwidth

0 T

B

Request <N, B(t)>

Q1: What are right model functions?

Q2: How to automatically derive the models?

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Challenges in Realizing TIVC

Q3: How to efficiently allocate TIVC?

Q4: How to enforce TIVC?

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Challenges in Realizing TIVC

• What are the right model functions?

• How to automatically derive the models?

• How to efficiently allocate TIVC?

• How to enforce TIVC?

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Challenges in Realizing TIVC

• What are the right model functions?

• How to automatically derive the models?

• How to efficiently allocate TIVC?

• How to enforce TIVC?

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How to Model Time-Varying BW?

Hadoop Hive Join

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TIVC Models

Virtual Cluster

T11 T32

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Hadoop Sort

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Hadoop Word Count

v

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Hadoop Hive Join

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Hadoop Hive Aggregation

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Challenges in Realizing TIVC

What are the right model functions?

• How to automatically derive the models?

• How to efficiently allocate TIVC?

• How to enforce TIVC?

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Possible Approach

• “White-box” approach– Given source code and data of cloud application,

analyze quantitative networking requirement– Very difficult in practice

• Observation: Many jobs are repeated many times– E.g., 40% jobs are recurring in Bing’s production data

center [Agarwal’12]– Of course, data itself may change across runs, but size

remains about the same

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Our Approach

• Solution: “Black-box” profiling based approach1. Collect traffic trace from profiling run2. Derive TIVC model from traffic trace

• Profiling: Same configuration as production runs– Same number of VMs– Same input data size per VM– Same job/VM configuration

How much BW should we give to the application?

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Impact of BW Capping

No-elongation BW threshold

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Choosing BW Cap

• Tradeoff between performance and cost– Cap > threshold: same performance, costs more– Cap < threshold: lower performance, may cost less

• Our Approach: Expose tradeoff to user1. Profile under different BW caps2. Expose run times and cost to user3. User picks the appropriate BW cap

Only below threshold ones

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From Profiling to Model Generation

• Collect traffic trace from each VM– Instantaneous throughput of 10ms bin

• Generate models for individual VMs

• Combine to obtain overall job’s TIVC model– Simplify allocation by working with one model– Does not lose efficiency since per-VM models are

roughly similar for MapReduce-like applications

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Generate Model for Individual VM

1. Choose Bb

2. Periods where B > Bb, set to BcapBW

Time

Bcap

Bb

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Maximal Efficiency Model

•

• Enumerate Bb to find the maximal efficiency model

Volume Bandwdith ReservedVolume Traffic nApplicatio

Efficiency BW

Time

Bcap

Bb

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Challenges in Realizing TIVC

What are the right model functions?

How to automatically derive the models?

• How to efficiently allocate TIVC?

• How to enforce TIVC?

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TIVC Allocation Algorithm

• Spatio-temporal allocation algorithm– Extends VC allocation algorithm to time dimension– Employs dynamic programming

• Properties– Locality aware– Efficient and scalable

• 99th percentile 28ms on a 64,000-VM data center in scheduling 5,000 jobs

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Challenges in Realizing TIVC

What are the right model functions?

How to automatically derive the models?

How to efficiently allocate TIVC?

• How to enforce TIVC?

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Enforcing TIVC Reservation

• Possible to enforce completely in hypervisor– Does not have control over upper level links– Requires online rate monitoring and feedback– Increases hypervisor overhead and complexity

• Observation: Few jobs share a link simultaneously– Most small jobs will fit into a rack– Only a few large jobs cross the core– In our simulations, < 26 jobs share a link in 64,000-VM

data center

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Enforcing TIVC Reservation

• Enforcing BW reservation in switches– Avoid complexity in hypervisors– Can be implemented on commodity switches

• Cisco Nexus 7000 supports 16k policers

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Challenges in Realizing TIVC

What are the right model functions?

How to automatically derive the models?

How to efficiently allocate TIVC?

How to enforce TIVC?

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Proteus: Implementing TIVC Models

1. Determine the model

2. Allocate and enforce the model

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Evaluation

• Large-scale simulation– Performance– Cost– Allocation algorithm

• Prototype implementation– Small-scale testbed

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Simulation Setup

• 3-level tree topology– 16,000 Hosts x 4 VMs– 4:1 oversubscription

• Workload– N: exponential distribution around mean 49 – B(t): derive from real Hadoop apps

50Gbps

10Gbps

…

… …1Gbps

…

20 Aggr Switch

20 ToR Switch

40 Hosts

… … …

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Batched Jobs

• Scenario: 5,000 time-insensitive jobs

42% 21% 23% 35%

1/3 of each type

Completion time reduction

All rest results are for mixed

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Varying Oversubscription and Job Size

25.8% reduction for non-oversubscribed

network

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Dynamically Arriving Jobs

• Scenario: Accommodate users’ requests in shared data center– 5,000 jobs, Poisson arrival, varying load

Rejected: VC: 9.5%

TIVC: 3.4%

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Analysis: Higher Concurrency

• Under 80% load

7% higher job concurrency

28% higher VM utilization

Rejected jobs are large

28% higher revenue

Charge VMs

V M

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Tenant Cost and Provider Revenue

• Charging model– VM time T and reserved BW volume B– Cost = N (kv T + kb B)

– kv = 0.004$/hr, kb = 0.00016$/GB

12% less cost for tenants Providers make

more money

Amazon target utilization

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Testbed Experiment

• Setup– 18 machines– Tc and NetFPGA rate

limiter

• Real MapReduce jobs

• Procedure– Offline profiling– Online reservation

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Testbed ResultTIVC finishes job faster than VC,

Baseline finishes the fastest

Baseline suffers elongation, TIVC achieves similar performance as VC

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Conclusion• Network reservations in cloud are important

– Previous work proposed fixed-BW reservations– However, cloud apps exhibit time-varying BW usage

• We propose TIVC abstraction – Provides time-varying network reservations– Uses simple pulse functions– Automatically generates model– Efficiently allocates and enforces reservations

• Proteus shows TIVC benefits both cloud provider and users significantly

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Backup slides

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Adding Cushions to Model

Without cushion With 60s cushion

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Network UtilizationVC reserves 26.4% abs.

more bandwidth

But less actual utilization (8.9% vs. 20.1%)

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BW Variability on Cloud

[Ballani’11]

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Model Refinement

• Can we further reduced BW for low efficiency pulses without elongation? – This allows us potentially fit more jobs

Hadoop Hive Join

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Model Refinement (cont.)

• If efficiency of a pulse < γ lower the cap so that efficiency = α• γ = 8%, α = 20%