Dynamic Thread Assignment onHeterogeneous Multiprocessor Architectures

Pree ThiengburanathumAdvanced computer architectureOct 24, 2007

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Agenda

•Introduction•Basic ideas and goals•Static versus Dynamic thread assignment•Architecture and Methodology•Results•Conclusion

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Introduction

•Multi programming •Chip multiprocessor (CMP)•Heterogeneous CMP system•Homogeneous CMP system

More processors cores in the single chip!

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Goals• Heterogeneous vs. Homogeneous CMP system

• What type of core should be replicated? Many simple cores = higher thread parallelism Fewer cores, larger = lower thread parallelism

• Multi-programmed computing environment may present threads of execution with different hardware resource requirements

maximize resource utilization & achieve a high degree of inter-thread parallelism.

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Basic ideas

•Taking advantage of Heterogeneous CMPMapping running tasksControl MechanismEasy to implement

Claim, a dynamic policy is more preferable than the static one.

•What is about a static policy?

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Scenario of heterogeneous CMP system (1)• Two processors P1 and P2 of different type• Assume that each program will run for 1 million

instructions• IPC = (Instructions) / (cycle)

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P1 P2

Thread A 1.6 0.4

Thread B 1.5 1

Table 1: IPC of threads A and B on cores P1 and P2

Scenario of heterogeneous CMP system(2)•Execution time = #instruction / IPC

•Moving the threads into different cores give the better total execution time.

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P1 P2

Thread A ~700,000 ~2,500,000

Thread B ~700,000 ~1,000,000

Table 2: Execution time of threads A and B on cores P1 and P2

Scenario of heterogeneous CMP system(3)•If we move thread A into P2 and thread B to P1

Total execution time = 2.5M•If we move thread A into P1 and thread B to P2 Total execution time = 1M

• The mapping programs to the core improve performance.• Assume programs can migrate across cores

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Dynamic thread assignment

•Thread assignment depends on the ratios between the IPCs on the two different core .

•The higher the ratios, the more the execution time.

•What is about thread assignment in homogenous CMP system?

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Simulation approach

•Real program and real processors.•SPEC2000 and Alpha

PerformanceNumber of cores and programsIPC number problems.Thread migration overhead.New assignment policies

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Processor configurations (1)

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Benchmark SPEC2000

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Benchmark of EV5 and EV6

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Processor configurations (2)

•homogeneous configurations: 4 EV6s or 20 EV5s

•heterogeneous configurations: 5 EV5s and 3EV6s 10 EV5s and 2 EV6s 15 EV5s and 1 EV6.

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CMP Simulation Model• To evaluate different combinations of

processors, workloads, and thread assignment policies.

• The model: working principles: A multiprocessor system can be thought of as a collection of processor and thread objects where each thread represents an instance of one of the benchmark programs.

• Modeling thread migrationinter-core context switch - the architectural state (PC value, registers, etc.) Use the parameter such as switch_duration and switch_loss

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Assignment Policies• Static Assignment• Well studies problem before assign• Solution rely on heuristics

• a random static assignment. Don’t know the work loads and IPC, always assign the faster core (EV6)

• a pseudo best static assignment. Know the work loads and IPC, use heuristic to find out.

• Disadvantages does not optimize EV6 usage slow” threads on EV5 penalize overall system

performance

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Assignment Policies

•Round robin dynamic assignment rotating the assignment of threads to processors

in a round robin fashion ensures that the available EV6 cores are equally

shared among the running programs.

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IPC driven dynamic assignment

•Considering the characteristics of the executing threads.

•Look at IPC number and ratio to decide•Thread with higher ratio run on EV6•Thread with lower ratio run on EV5

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Simulation results (1)

•Homogeneous vs. heterogeneous configuration with static assignment

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Simulation results (2)

•Dynamic assignment

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Conclusion

•Dynamic thread assignment increase performance and usage.

outperform a random assignment policy by 20% to 40%

outperform a homogeneous configuration by 20% to 80%

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Bibliography • [1] B. Michael, C. Patrick. “Dynamic Thread Assignment on

Heterogeneous Multiprocessor Architectures”, Conference on computing frontiers, Proceedings the 3rd conference on computing systems, page 29-40, May 2006

• [2] Silberschatz, Gavin, Gagne. “Operating system concepts sixth edition”, 2004

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Question?

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