the only constant is change: incorporating time-varying bandwidth reservations in data centers di...
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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%