ammm

Multi-core architectures
Jac
Single-core computer

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Single-core CPU chip the single core

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Multi-core architectures
• This lecture is about a new trend in computer architecture:
Replicate multiple processor cores on a single die.
Core 1

Multi-core CPU chip

Core 2

Core 3

Core 4

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Multi-core CPU chip
• The cores fit on a single processor socket
• Also called CMP (Chip Multi-Processor)

c o r e c o r e c o r e c o r e 1

2

3

4

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The cores run in parallel thread 1

thread 2

thread 3

thread 4

c o r e c o r e c o r e c o r e 1

2

3

4

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Within each core, threads are time-sliced
(just like on a uniprocessor) several threads

several threads several threads several threads c o r e c o r e c o r e c o r e 1

2

3

4

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Interaction with the
Operating System
• OS perceives each core as a separate processor
• OS scheduler maps threads/processes to different cores
• Most major OS support multi-core today:
Windows, Linux, Mac OS X, …

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Why multi-core ?
• Difficult to make single-core clock frequencies even higher
• Deeply pipelined circuits:
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heat problems speed of light problems difficult design and verification large design teams necessary server farms need expensive air-conditioning • Many new applications are multithreaded
• General trend in computer architecture (shift towards more parallelism)

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Instruction-level parallelism
• Parallelism at the machine-instruction level
• The processor can re-order, pipeline instructions, split them into microinstructions, do aggressive branch prediction, etc.
• Instruction-level parallelism enabled rapid increases in processor speeds over the last 15 years
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Thread-level parallelism (TLP)
• This is parallelism on a more coarser scale
• Server can serve each client in a separate
thread