parallel real -time scheduling from theory to implementationalp514/hpc2017/jing_li.pdf · snippet...

ParallelReal-TimeSchedulingfromTheorytoImplementation

Jing LiDepartmentofComputerScienceYingWuCollegeofComputing

New Jersey Institute of [email protected]

OutlineØ Why do we demand parallelism?

Ø My research: exploiting parallelism in real-time systems

Ø Two examples of my research

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FutureofComputingPerformance

100

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1970 1980 1990 2000 2010 2020

Frequency (MHz)

Year

40 Years of Microprocessor Trend Data

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Originaldatauptotheyear2010collectedandplottedbyM.Horowitz,F.Labonte,O.Shacham,K.Olukotun, L.Hammond,andC.Batten.Newplotanddatacollectedfor2010-2015byK.Rupp.

ThefastestslothworkingattheDMV (from Zootopia).

PowerDensityØ Clock frequency hits the power wall.

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Multi-CoreSystems

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1970 1980 1990 2000 2010 2020

Number of

Logical Cores

Frequency (MHz)

Year

40 Years of Microprocessor Trend Data

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Originaldatauptotheyear2010collectedandplottedbyM.Horowitz,F.Labonte,O.Shacham,K.Olukotun, L.Hammond,andC.Batten.Newplotanddatacollectedfor2010-2015byK.Rupp.

Multi-Core=Parallelism?Ø Concurrent execution of jobs

Ø Parallel execution of a job

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coressinglemulti-coremachine

jobs Job 1 Job 2 Job 3


jobs

LaneKeepingAssistSystem in Cars

Since the system interacts with the physical world, its computation must be completed under a time constraint.

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Applications Benefit from Intra-Job ParallelismØ Motion planning program in a self-driving car

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FromKimetal.[ICCPS13]

Cyber-Physical Systems(CPS)CPS are built from, and depend upon, the seamless integration of computational algorithms and physical components.

E.g., robotics, drones, autonomous vehicles, etc. 9

Applications Benefit from Intra-Job Parallelism

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Searchtheweb

*Jeff Dean et al.(Google) "Thetailatscale."CommunicationsoftheACM56.2(2013)

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Response

Query

Ø Web searchNeed to respond within100msfor users to find responsive*.

InteractiveCloudServices(ICS)E.g., web search, online gaming, stock trading etc.

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Searchtheweb

Real-Time SystemsThe performance of the systems depends not only upon theirfunctional aspects, but also upon their temporal aspects.

Real-time performance:

1) Provide hard guarantee of meeting jobs’ deadlines (e.g. CPS)2) Optimize latency-related objectives for jobs (e.g. ICS)

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NewGenerationofReal-TimeSystemsCharacteristics:

Ø New classes of applications with complex functionalitiesØ Increasing computational demand of each application

Ø Consolidating multiple applications onto a shared platform Ø Rapid increase in the number of cores per chip

Demand: leverage parallelism within the applications, to improve real-time performance and system efficiency

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Myresearch:parallelreal-timescheduling from theory to implementation



Ø Example 1: parallel real-time scheduling for meeting deadlines

Ø Example 2: parallel real-time scheduling for a target latency

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Real-TimeHybridSimulation(RTHS)

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Since the numerical simulation interacts with the physical specimen, its computation must be completed by its deadline.

Cyber-PhysicalBoundary

^RobertL.andTerryL.BowenLargeScaleStructuresLaboratoryatPurdueUniversity

Numericalsimulation Physicalspecimen

HowtoAllocateCorestoMultipleParallelJobs?Ø A real world system consists of many parallel jobs

Ø Each job demands different real-time performanceq E.g., jobs need to meet their deadlines in RTHS

Ø The goal of parallel real-time scheduling:smartly allocate cores to parallel jobs to meet their deadlines

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jobs

HowtoAnalyzeaParallelJob?Ø An example:

Computation on a array A[i] with m elements

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m=3

int i = 0;

parallel_for (; i < m; i++) {compute( A[i] );

}bar();

Naturally captures programs generated

by parallel languages such as Cilk Plus, Intel TBB and OpenMP.

Node: sequential computation

Edge: dependence between nodes

DirectedAcyclicGraph (DAG) Model

Unitnode– singleinstruction

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available nodecompleted nodeunavailable node


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Work T1 : execution time on one coreSpan T∞ : execution time on ∞ cores

(critical-path length)

Work and Span

T1 =18T∞ =9

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FederatedSchedulingFor parallel tasks, FS has the best bound in term of schedulability

FS assigns ni dedicated cores to each parallel task

ni – the minimum #cores needed for a task to meet its deadline

cores

𝑛" =𝐶" − 𝐿"𝐷" − 𝐿"

deadlineDi =periodworst-case span Liworst-case workCi

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tasks

FSPlatformØ Middleware platform providing FS service in Linux

Ø Work with GNU OpenMP runtime system Ø Run OpenMP programs with minimum modification

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cores

Linux

FederatedScheduling(FS)

OpenMPRuntime

OpenMPRuntime

OpenMPRuntime

ParallelismImprovesRTHSAccuracy

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A RTHS simulates a nine stories building, with first story damper

Ø Previously, sequential processing power limits a rate of 575HzØ Parallel execution now allows a rate of 3000Hz

Ø Reduction in error for acceleration and displacement

Ø Parallelism increases accuracy via faster actuation and sensing

Sequential (575Hz)Parallel(3000Hz)

Time(sec)

Normalize

dError(%)



Ø Example 1: parallel real-time scheduling for meeting deadlines

Ø Example 2: parallel real-time scheduling for a target latency

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SystemforInteractiveCloudServicesOnline system: do not know when jobs arrive

Objective: maximize the number of jobs that meet a target latency T

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WorkloadDistributionHasaLongTail

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Job SequentialExecutionTime(ms)(work)

Bing searchworkload

Ø Large jobs must run in parallel to meet target latency

Ø Always run large jobs in full parallelism?

Target latency

Parallelize Large Jobs According to LoadTail-Control Strategy: when load is low, run all jobs in parallel; when load is high, run large jobs sequentially.

Latency = Processing Time + Waiting time

At low load: processing time dominates latency

At high load:waiting time dominates latency

time

core1

core2

core3

✔Miss0 request

core1

core2

core3time

✔Miss1 request

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target

target

TheInnerWorkingsofTail-ControlWe implement tail-control algorithm in the runtime system of Intel Thread Building Block and evaluate on Bing search workload.

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We implement tail-control algorithm in the runtime system of Intel Thread Building Block and evaluate on Bing search workload.

TheInnerWorkingsofTail-Control

TargetLatency

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defaultwork-stealing≥


TargetLatency

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TargetLatency

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ConclusionExploit the untapped efficiency in parallel computing platforms and drastically improve the real-time performance of applications.

Ø System Guaranteed to Meet Deadlines for CPSq Develop provably good schedulers for parallel applications

q Incorporate real-time scheduling into parallel runtime system

Ø System Optimized to Meet Target Latency for ICSq Design and implement strategy to optimize real-time performance

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parallel real -time scheduling from theory to implementationalp514/hpc2017/jing_li.pdf · snippet...

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