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Parallel computing and its recent topics

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Outline

1. Introduction of parallel processing 　(1) What is parallel processing(2) Classification of parallel processing

2. Foundation of parallel computing 　 (1) Parallel computational model: PRAM (Parallel Random Access Machine) (2) Analysis of parallel algorithms

3. Design of parallel algorithms (1) Basic techniques

(2) Divide-and-conquer 4. Current trend of parallel processing (1) Cluster computing (2) Grid computing

　

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Reference

•　 J. JaJa, "An Introduction to parallel algorithm" Addison-Wesley Publishing Company, 1992.

Questions to wchen@tnstate.edu

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Part 1 Introduction to parallel processing

Why Parallel Processing Problems with large computing complexity

•　 Computing hard problems (NP-complete problems): exponential computing time.

• Problems with large scale of input size: quantum chemistry, statistic mechanics,

relative physics, universal physics, fluid mechanics, biology, genetics engineering, …

For example, it costs 1 hour using the current computer to simulate the procedure

of 1 second reaction of protein molecule and water molecule. It costs

reaction.hour 1 of procedure thesimulate to years1014.1 8

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Why parallel processing

Physical limitation of CPU computational power

　 In past 50 years, CPU was speeded up double every 2.5 years. But, there are a physical limitation. Light speed is

Therefore, the limitation of the number of CPU clocks is expected to be about 10GHz.

To solve computing hard problems

•　 Parallel processing

•　 DNA computer

•　 Quantum computer

…

.sec/103 8m

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What is parallel processing

•　 Using a number of processors to process one task•　 Speeding up the processing by distributing it to the processors One problem

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Classification of parallel computers

Two kinds of classification１． Flann’s Classification•　 SISD (Single Instruction stream, Single Data stream)•　 MISD (Multiple Instruction stream, Single Data stream)•　 SIMD (Single Instruction stream, Multiple Data stream)•　 MIMD (Multiple Instruction stream, Multiple Data stream)

2. Classification by memory status• Share memory• Distributed memory 　

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Flynn’s classification(1)

SISD (Single Instruction Single Data) computer• Von Neuman’s one processor computer

Control Processor MemoryInstruction Stream

Data Stream

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Flynn’s classification (2)

MISD (Multi Instructions Single Data) computer 　All processors share a common memory, have their own control devices and execute their own instructions on same data.

Memory

Control ProcessorInstruction

Stream

Data Stream

Control Processor

Instruction Stream

Control Processor

Instruction Stream

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Flynn’s classification (3)

SIMD (Single Instructions Multi Data) computer• Processors execute the same instructions on different data • Operations of processors are synchronized by global clock.

Shared Memory or Inter- connection Nerwork

ProcessorData Stream

ControlProcessor

Instruction Stream

Processor

Data Stream

Data Stream

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Flynn’s classification (4)

MIMD (Multi Instruction Multi Data) Computer • Processors have their own control devices, and execute

different instructions on different data.• Operations of processors are executed asynchronously

in most time. • It is also called as distributed computing system.

Shared Memory or Inter- connection Nerwork

ProcessorData Stream

Processor

ControlInstruction

Stream

Processor

Data Stream

Data Stream

ControlInstruction

Stream

ControlInstruction

Stream

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Classification by memory types (1)

1. Parallel computer with a shared common memory •　 Communication based on shared memory For example, consider the case that processor i sends some data to processor j. First, processor i writes the data to the share memory, then processor j reads the data from the same address of the share memory.

Shared Memory

Processor

Processor

Processor

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Classification by memory types (2)

Features of parallel computers with shared common memory 　

•　 Programming is easy.

• Exclusive control is necessary for the access to the same memory cell. 　

• Realization is difficult when the number of processors is large.

（ Reason) The number of processors connected to shared memory is limited by

the physical factors such as the size and voltage of units, and the latency cause

d in memory accessing.

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Classification by memory tapes (3)

2. Parallel computers with distributed memoryCommunication style is one to one based on interconnection network. For example, consider the case that processor i sends data to processor j. First, processor i issues a send command such as “processor j sends xxx to process i”, then processor j gets the data by a receiving command.

Inter- connection Nerwork

Processor Local Memory

Processor Local Memory

Processor Local Memory

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Classification by memory types (4)

Features of parallel computers using distributed

memory • There are various architectures of interconnection

networks (Generally, the degree of connectivity is not large.) • Programming is difficult since comparing with shared

common memory the communication style is one to one. • It is easy to increase the number of processors.

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Types of parallel computers with distributed memory

Complete connection type Any two processors are connected Features

Strong communication ability, but not practical (each processor has to be connected to many processors).

Mash connection type Processors are connected as a two-dimension lattice. Feartures - Connected to few processors. Easily to increase

the number of processors.– Large distance between processors: 　– Existence of processor communication bottleneck.

P1

P2 P5

P3 P4

P0,0 P0,1 P0,2 P0,3

P1,0 P1,1 P1,2 P1,3

P2,0 P2,1 P2,2 P2,3

P3,0 P3,1 P3,2 P3,3

n

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　Hypercube connection type

Processors connected as a hypercube (each processor has a binary number. (Processors are connected if only if one bit of their number are different. ）

Features• Small distance between processors: log n.• Balanced communication load because of its symmetric structure.• Easy to increase the number of processors.

0100

0101

0110

0111

1100

1101

1110

1111

0000

0001

0010

0011

1000

1001

1010

1011

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Other connected type Tree connection type, butterfly connection type, bus connection type. Criterion for selecting an inter-connection network •　 Small diameter (the largest distance between processors) for small communication delay. •　 Symmetric structure for easily increasing the number of processors.

The type of inter-connection network depends on application, ability of processors, upper bound of the number of processors and other factors.

The type of inter-connection network depends on application, ability of processors, upper bound of the number of processors and other factors.

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Real parallel processing system (1)

Early days parallel computer (ILLIAC IV)•　 Built in 1972•　 SIMD type with distributed memory, consisting of 64 processors

P0,0 P0,1 P0,2 P0,3

P1,0 P1,1 P1,2 P1,3

P2,0 P2,1 P2,2 P2,3

P3,0 P3,1 P3,2 P3,3

Transformed mash connection type, equipped with common data bus, common control bus, and one controlUnit.

Transformed mash connection type, equipped with common data bus, common control bus, and one controlUnit.

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Real parallel processing system (2)

Parallel computers in recent days•　 Shared common memory type

Workstation, SGI Origin2000 and other with 2-8 processors. •　 Distributed memory type

Name Maker Processor num

Processing type Network type

CM-2 TM 65536 SIMD hypercube

CM-5 TM 1024 MIMD fat tree

nCUBE2 NCUBE 8192 MIMD hypercube

iWarp CMU, Intel 64 MIMD 2D torus

Paragon Intel 4096 MIMD 2D torus

SP-2 IBM 512 MIMD HP switch

AP1000 Fujitsu 1024 MIMD 2D torus

SR2201 Hitachi 1024 MIMD crossbar

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Real parallel processing system (3)

Deep blue•　 Developed by IBM for chess game only •　 Defeating the chess champion •　 Based on general parallel computer SP-2

memory

RS/6000 Bus Interface

Microchannel Bus

Deep blue chip

Deep blue chip

Deep blue chip（ 8個）

RS/6000

node

memory

RS/6000

node

RS/6000

node

（ 32 nodes）

Inter-connection network (Generalized hypercube)

memory memory

Architecture of nodes

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Problems in parallel processing

(1) Large cost(2) Long developing period

(3) Programming difficulties

• Comparing with sequential processing, programming is complicat

ed, especially for distributed memory type.

• Debug is hacrd (tracing is necessary for all the processors).