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Multi-core ArchitectureMulti-core ArchitectureGV: Nguyễn Tiến Dũng

Sinh viên: Ngô Quang Thìn Nguyễn Trung Thành Trần Hoàng Điệp

Lớp: KSTN-ĐTVT-K52

ContentsContents

Background1

Multi-core basics2

Multi-core challenges3

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1. Background1. Background

1.1 Brief history of Microprocessor

1.2 Moore’s Law

1.3 Past efforts to increase efficiency

1.4 The need for Multi-core

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1.1 Brief history of Microprocessors1.1 Brief history of Microprocessors

Early 1970s: 4-bit 4004 (Intel)

8-bit:8008 & 8080 (Intel), 6800 (Motorola)

16-bit: 8086 & 8088 (Intel), 68000 (Motorola)

32-bit: 80386 (Intel)

Pentium,… (Intel)

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1.2 Moore’s Law1.2 Moore’s Law

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1.3 Past efforts to increase efficiency1.3 Past efforts to increase efficiency

• Microprocessor frequency was synonymous with performance

-> increase in processor frequency

Pentium 4: 1.3 – 3.8 GHz over 8 years• Multiple instruction

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1.3 Past efforts to increase efficiency1.3 Past efforts to increase efficiency

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1.4 The need for Multi-core1.4 The need for Multi-core

• Two cores processor: twice the performance and dissipate less heat than the fastest single core processor.

• 2005, IEEE review: “power consumption increase by 60% with every 400MHz rise in clock speed…But the dual-core approach means you can get a significant boost in performance without the need to run at ruinous clock rates”

• Some experts believe that “ by 2017 embedded processors could sport 4096 cores, server CPUs might have 512 cores and desktop chips could use 128 cores” → So astounding!!!

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2. Multi-core basics2. Multi-core basics

Basic configuration of a microprocessor

Level 1 (L1) Cache: store data frequently used by the processor

L2 cache: lager than L1Main memory: very large, slower

than cacheCommunication method: single

communication bus (shared memory model) or interconnection network (distributed memory model)

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2. Multi-core basics (cont…)2. Multi-core basics (cont…)

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2. Multi-core basics (cont…)2. Multi-core basics (cont…)

the single core

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2. Multicore basics (cont…)2. Multicore basics (cont…)

Multi-core architecture:

Core 1 Core 2 Core 3 Core 4

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2. Multi-core basics (cont…)2. Multi-core basics (cont…)

core

1

core

2

core

3

core

4

thread 1 thread 2 thread 3 thread 4

The cores run in parallel

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2. Multi-core basics (cont…)2. Multi-core basics (cont…)

Comparison of a single and multi-core (8 cores) processor used by the Packaging Research Center at Georgia Tech

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3. Multi-core Challenges3. Multi-core Challenges

Power and temperature managementMemory/cacheProgramming for multi-core

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3.1 Power and Temperature3.1 Power and Temperature

2 cores were placed on a single chip

→consume twice as much power and generate a large amount of heat

→computer may combustThe chip is architected: number of hot spots doesn’t

grow too large and the heat is spread out across the chip

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3.1 Power and Temperature (cont…)3.1 Power and Temperature (cont…)

Heat in the CELL processor is dissipated in the Power Processing Element and the rest is spread across the Synergistic Processing Elements.

Monitor temperature in the Chip by one linear sensor and ten internal digital sensor

Since we have private caches: How to keep the data consistent across caches?

→Each core should perceive the memory as a monolithic array, shared by all the cores

3.2 Cache Coherence 3.2 Cache Coherence

Core 1 Core 2 Core 3 Core 4

One or more levels of

cachex=1

One or more levels of

cachex=1

One or more levels of

cache

One or more levels of

cache

Main memoryx=1

multi-core chip

3.2 Cache Coherence

Core 2 reads xCore 1 reads x

Core 1 writes to x, setting it to 2

Core 1 Core 2 Core 3 Core 4

One or more levels of

cachex=2

One or more levels of

cachex=1

One or more levels of

cache

One or more levels of

cache

Main memoryx=2

multi-core chipassuming write-through

caches

3.2 Cache Coherence

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Core 2 attempts to read x… gets a stale copy

Core 1 Core 2 Core 3 Core 4

One or more levels of

cachex=2

One or more levels of

cachex=1

One or more levels of

cache

One or more levels of

cache

Main memoryx=2

multi-core chip

3.2 Cache Coherence

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3.2 Cache Coherence3.2 Cache Coherence

Solutions for cache coherenceThis is a general problem with multiprocessors, not

limited just to multi-coreThere exist many solution algorithms, coherence

protocols, etc.

A simple solution: invalidation-based protocol with snooping

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Inter-core busInter-core bus

Core 1 Core 2 Core 3 Core 4

One or more levels of

cache

One or more levels of

cache

One or more levels of

cache

One or more levels of

cache

Main memory multi-core chip

inter-core bus

3.2 Cache Coherence

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Revisited: Cores 1 and 2 have both read x

Core 1 Core 2 Core 3 Core 4

One or more levels of

cachex=1

One or more levels of

cachex=1

One or more levels of

cache

One or more levels of

cache

Main memoryx=1

multi-core chip

3.2 Cache Coherence

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Core 1 writes to x, setting it to 2

Core 1 Core 2 Core 3 Core 4

One or more levels of

cachex=2

One or more levels of

cachex=1

One or more levels of

cache

One or more levels of

cache

Main memoryx=2

multi-core chipassuming write-through

caches

INVALIDATEDsendsinvalidation

request

inter-core bus

3.2 Cache Coherence

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After invalidation:

Core 1 Core 2 Core 3 Core 4

One or more levels of

cachex=2

One or more levels of

cache

One or more levels of

cache

One or more levels of

cache

Main memoryx=2

multi-core chip

3.2 Cache Coherence

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Core 2 reads x. Cache misses, and loads the new copy.

Core 1 Core 2 Core 3 Core 4

One or more levels of

cachex=2

One or more levels of

cachex=2

One or more levels of

cache

One or more levels of

cache

Main memoryx=2

multi-core chip

3.2 Cache Coherence

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3.2 Cache Coherenceupdate protocol

Core 1 writes x=2:

Core 1 Core 2 Core 3 Core 4

One or more levels of

cachex=21660

One or more levels of

cachex=21660

One or more levels of

cache

One or more levels of

cache

Main memoryx=21660

multi-core chipassuming write-through

caches

UPDATED

broadcastsupdatedvalue inter-core bus

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3.2 Cache Coherence

Which do you think is better? Invalidation or update?

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• Multiple writes to the same location– invalidation: only the first time– update: must broadcast each write (which includes

new variable value)

• Invalidation generally performs better: it generates less bus traffic

3.2 Cache Coherence

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3.3 Programming for multi-core3.3 Programming for multi-core

Programmers must use threads or processes

Spread the workload across multiple cores

Write parallel algorithms

OS will map threads/processes to cores

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3.3 Programming for multi-core3.3 Programming for multi-core

Thread safety very importantPre-emptive context switching: context switch can

happen AT ANY TIME

→ Need to use synchronization

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3.3 Programming for multi-core3.3 Programming for multi-core

Example:int counter=0;void thread1() { int temp1=counter; counter = temp1 + 1;}void thread2() { int temp2=counter; counter = temp2 + 1;}

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temp1=counter;counter = temp1 + 1;temp2=counter;counter = temp2 + 1

temp1=counter;temp2=counter;counter = temp1 + 1;counter = temp2 + 1

gives counter=2

gives counter=1

3.3 Programming for multi-core3.3 Programming for multi-core

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3.3 Programming for multi-core3.3 Programming for multi-core

→ Assigning threads to the cores

Each thread/process has an affinity mask

Affinity mask specifies what cores the thread is allowed to run on

Different threads can have different masks

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3.3 Programming for multi-core3.3 Programming for multi-core

Example: 4-way multi-core, without SMT

1011

core 3 core 2 core 1 core 0

Process/thread is allowed to run on cores 0,2,3, but not on core 1

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Multi-core chips an important new trend in computer architecture

Several new multi-core chips in design phases

Parallel programming techniques

likely to gain importance

ConclusionConclusion

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