Multi-Core Computing

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Multi-Core Computing

• Ahmad Aljebaly
• Department of Computer Science
• Western Michigan University

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Agenda

• Introduction
• Motivation for Multi-Core
• What is multi-core processor?
• Properties of Multi-core systems
• Applications benefit from multi-core
• Multiprocessor memory types
• Multi-core design
• Symmetric multi-core processor
• Asymmetric multi-core processor
• Advantages disadvantages of multi-core

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Introduction

• First Microprocessor(1970s)
• Intel 4004
• PC spreads in the world(1980s)
• Up to 32bits microprocessor
• AMD followed Intels technology

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Introduction

• Flood of Computer Tasks(1990s)
• Increasing of Computer user
• Server management ? Construct the database
• We need better performance of PC or Server.
• ? These demands accelerate the development of
  microprocessor.
• Emergence of Multi-core Processor(2000s)
• Limits of improvement of single core
• Turn over of the idea that improve the MP
  technology
• Put execution cores in one die

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Motivation for Multi-Core

• Exploits increased feature-size and density
• Increases functional units per chip (spatial
  efficiency)
• Limits energy consumption per operation
• Constrains growth in processor complexity

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Multi-Core Computer

• A multi-core processor is a processing system
  composed of two or more independent cores (or
  CPUs). The cores are typically integrated onto a
  single integrated circuit die (known as a chip
  multiprocessor or CMP), or they may be integrated
  onto multiple dies in a single chip package.
• A many-core processor is one in which the number
  of cores is large enough that traditional
  multi-processor techniques are no longer
  efficient - this threshold is somewhere in the
  range of several tens of cores - and likely
  requires a network on chip.

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Multi-Core Computer

• dual-core processor contains two independent
  microprocessors.
• A dual core set-up is somewhat comparable to
  having multiple, separate processors installed in
  the same computer, but because the two processors
  are actually plugged into the same socket, the
  connection between them is faster. Ideally, a
  dual core processor is nearly twice as powerful
  as a single core processor. In practice,
  performance gains are said to be about fifty
  percent a dual core processor is likely to be
  about one-and-a-half times as powerful as a
  single core processor.

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Multi-Core Computer

• A multi-core processor implements multiprocessing
  in a single physical package. Cores in a
  multi-core device may be coupled together tightly
  or loosely. For example, cores may or may not
  share caches, and they may implement message
  passing or shared memory inter-core communication
  methods. Common network topologies to
  interconnect cores include bus, ring,
  2-dimentional mesh, and crossbar.
• All cores are identical in symmetric multi-core
  systems and they are not identical in asymmetric
  multi-core systems. Just as with single-processor
  systems, cores in multi-core systems may
  implement architectures such as superscalar,
  vector processing, or multithreading.

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Multi-Core Computer

• Multi-core processors are widely used across many
  application domains including general-purpose,
  embedded, network, digital signal processing, and
  graphics.
• The amount of performance gained by the use of a
  multi-core processor is strongly dependent on the
  software algorithms and implementation.
• Multi-core processing is a growing industry trend
  as single core processors rapidly reach the
  physical limits of possible complexity and speed.
  
• Companies that have produced or are working on
  multi-core products include AMD, ARM, Broadcom,
  Intel, and VIA.

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CMP benefits

• with a shared on-chip cache memory, communication
  events can be reduced to just a handful of
  processor cycles.
• therefore with low latencies, communication
  delays have a much smaller impact on overall
  performance.
• threads can also be much smaller and still be
  effective.
• automatic parallelization more feasible.

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Properties of Multi-core systems

• Cores will be shared with a wide range of other
  applications dynamically.
• Load can no longer be considered symmetric across
  the cores.
• Cores will likely not be asymmetric as
  accelerators become common for scientific
  hardware.
• Source code will often be unavailable, preventing
  compilation against the specific hardware
  configuration.

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What applications benefit from multi-core?

• Database servers
• Web servers
• Telecommunication markets
• Multimedia applications
• Scientific applications
• In general, applications with Thread-level
  parallelism (as opposed to instruction-level
  parallelism)

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Multi-core architectures

• Replicate multiple processor cores on a single
  die.

• The cores fit on a single processor socket.

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The cores run in parallel(like on a uniprocessor)
several threads
several threads
several threads
several threads
core 1
core 2
core 3
core 4
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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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Interaction with OS

• Most major OS support multi-core today.
• OS perceives each core as a separate processor.
• OS scheduler maps threads/processes to different
  cores.

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Examples

• Editing a photo while recording a TV show through
  a digital video recorder.
• Downloading software while running an anti-virus
  program.
• Anything that can be threaded today will map
  efficiently to multi-core.
• BUT some applications difficult to parallelize.

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Why Multi-core?

• Better Performance
• For the Multi tasking
• e.g. Burning CD with graphic works at the same
  time
• Power consumption and Heat generation
• Caused from the advance of CPU clock speed

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Why Multi-core?

• Save the room of motherboard
• Two single cores ? In one die
• We can use this room more efficiently
• Simplicity
• We need additional systems to control the several
  single cores.
• Economical efficiency
• A dual-core is much cheaper than two single cores

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Multiprocessor memory types

• Shared memoryIn this model, there is one
  (large) common shared memory for all processors.
• Distributed memoryIn this model, each processor
  has its own (small) local memory, and its content
  is not replicated anywhere else.

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Microprocessor Design

• Taking the idea of superscalar operations to the
  next level, it is possible to put multiple
  microprocessor cores onto a single chip, and have
  the cores operate in parallel with one another.

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Symmetric Multi-core Processor(SMP)

• A symmetric multi-core processor is one that has
  multiple cores on a single chip, and all of those
  cores are identical.
• Example Intel Core 2
• The Intel Core 2 is an example of a symmetric
  multi-core processor. The Core 2 can have either
  2 cores on chip ("Core 2 Duo") or 4 cores on chip
  ("Core 2 Quad"). Each core in the Core 2 chip is
  symmetrical, and can function independently of
  one another. It requires a mixture of scheduling
  software and hardware to farm tasks out to each
  core.

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Symmetric Multi-core Processor
All cores which exist in a die are exactly
identical
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Symmetric Multi-core Processor

• A symmetric multi-core processor is a processor
  which has multiple cores that are all exactly the
  same. Every single core has the same architecture
  and the same capabilities.
• Each core has the same capabilities, so it
  requires that there is an arbitration unit to
  give each core a specific task. Software that
  uses techniques like multithreading makes the
  best use of a multi-core processor like the Intel
  Core2.

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Symmetric Multi-core Processor

• Applications
• Personal Computers

• Server / Super Computer

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Asymmetric Multi-core Processor

• An asymmetric multi-core processor is one that
  has multiple cores on a single chip, but those
  cores might be different designs. For instance,
  there could be 2 general purpose cores and 2
  vector cores on a single chip.
• Example Cell Processor
• IBM's Cell processor, used in the Sony
  PlayStation 3 video game console is an
  asymmetrical multi-core processor. The Cell has 9
  processor cores on board, one general purpose
  processor, and 8 data-processing cores. The one
  multipurpose core, known as the Power Processor
  Element (PPE) controls the communication between
  the other cores, and distributes computing tasks
  to the other cores for processing. The other 8
  cores are known as Synergistic Processor Elements
  (SPE), and are specially designed to have high
  floating-point throughput, especially with vector
  operations.

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Asymmetric Multi-core Processor

• In an asymmetric multi-core processor, the chip
  has multiple cores onboard, but the cores might
  be different designs.
• Each core will have different capabilities.

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Example IBM Cell Processor

• An example of an asymmetric multi-core processor
  is the IBM Cell processor.

• The IBM Cell processor has 1 Power Processor
  Element (PPE) that controls the chip, and 8
  Synergistic Processor Elements (SPEs) that are
  designed for high mathematical throughput. The
  IBM Cell processor is designed as follows

Notice how the SPE cores only connect to the PPE,
and not to each other. Notice also that the PPE
core is much larger then the individual SPE cores.
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Asymmetric Multi-core Processor(ASMP) Cell
Processor

• Applications
• Super Computing
• IBM's latest supercomputer, IBM Roadrunner, is a
  hybrid of General Purpose CISC Opteron as well as
  Cell processors.

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Asymmetric Multi-core Processor(ASMP) Cell
Processor

• Applications
• Home cinema
• Toshiba is considering producing HDTVs using
  Cell. They have already presented a system to
  decode 48 standard definition MPEG-2 streams.
  This can enable a viewer to choose a channel
  based on dozens of thumbnail videos displayed on
  the screen in the same time.

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Asymmetric Multi-core Processor(ASMP) Cell
Processor

• Applications
• Video Processing Card
• Some companies, such as Leadtek, have plans to
  release a PCI-E card based upon the Cell to allow
  for "faster than real time" transcoding of H.264,
  MPEG-2 and MPEG-4 video.

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Asymmetric Multi-core Processor(ASMP) Cell
Processor

• Applications
• Console Video Games
• The first major commercial application of Cell
  was in Sony's PlayStation 3 game console.
• This video game console contains the first
  production application of the Cell processor,
  clocked at 3.2 GHz and containing seven out of
  eight operational SPEs, to allow Sony to increase
  the yield on the processor manufacture. Only six
  of the seven SPEs are accessible to developers as
  one is reserved by the OS.

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Asymmetric Multi-core Processor(ASMP) Cell
Processor

• Future
• Based on the unique features, Cell can bridge the
  gap between conventional desktop processors (such
  as the Athlon 64, and Core 2 families) and more
  specialized high-performance processors, such as
  the NVIDIA and ATI graphics-processors (GPUs).
• Cell will expand its intended use in current and
  future digital distribution systems, as well as
  in high-definition displays and recording
  equipment and computer entertainment systems.

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Multi-Core Computer

• Future of the SMP (Related to ASMP)
• Easy to implement that lots of cores put in one
  integrated circuit
• Easier programming than ASMP
• Because all the cores are identical
• Easy to keep the development speed
• Apply to any type of system (General usage)

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Multi-Core Computer

• Future of the SMP (Related to ASMP)
• Not proper to certain specific system
• Audio/video processing, data compression, and so
  on
• Waste the silicon and power
• Because it is made for the general purpose
• Less efficiency than ASMP
• These are reasons why ASMP has emerged .

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Challenges resulting from multi-core

• Relies on effective exploitation of
  multiple-thread parallelism
• Need for parallel computing model and parallel
  programming model
• Aggravates memory wall
• Memory bandwidth
• Way to get data out of memory banks
• Way to get data into multi-core processor array
• Memory latency
• Fragments L3 cache
• Pins become strangle point
• Rate of pin growth projected to slow and flatten
• Rate of bandwidth per pin (pair) projected to
  grow slowly
• Requires mechanisms for efficient inter-processor
  coordination
• Synchronization
• Mutual exclusion
• Context switching

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Advantages of Multi-core

• Cache coherency circuitry can operate at a much
  higher clock rate than is possible if the signals
  have to travel off-chip.
• Signals between different CPUs travel shorter
  distances, those signals degrade less.
• These higher quality signals allow more data to
  be sent in a given time period since individual
  signals can be shorter and do not need to be
  repeated as often.
• A dual-core processor uses slightly less power
  than two coupled single-core processors.

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Disadvantages of Multi-core

• Ability of multi-core processors to increase
  application performance depends on the use of
  multiple threads within applications.
• Most Current video games will run faster on a 3
  GHz single-core processor than on a 2GHz
  dual-core processor (of the same core
  architecture.
• Two processing cores sharing the same system bus
  and memory bandwidth limits the real-world
  performance advantage.
• If a single core is close to being memory
  bandwidth limited, going to dual-core might only
  give 30 to 70 improvement.
• If memory bandwidth is not a problem, a 90
  improvement can be expected.

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Conclusion

• All computers are now parallel computers!
• Multi-core processors represent an important new
  trend in computer architecture.
• Decreased power consumption and heat generation.
• Minimized wire lengths and interconnect
  latencies.
• They enable true thread-level parallelism with
  great energy efficiency and scalability.
• To utilize their full potential, applications
  will need to move from a single to a
  multi-threaded model.
• Parallel programming techniques likely to gain
  importance.
• the difficult problem is not building multi-core
  hardware, but programming it in a way that lets
  mainstream applications benefit from the
  continued exponential growth in CPU performance.
• the software industry needs to get back into the
  state where existing applications run faster on
  new hardware.

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References

• http//en.wikipedia.org/wiki/Multi-core_(computing
  )
• Olukotun, Kunle and Hammond, Lance. The future of
  microprocessors.Queue, Volume 3, Issue 7,
  September 2005.
• www.princeton.edu/jdonald/research/hyperthreading
  /garg_report.pdf
• Zheltov, Sergey N. and Bratanov, Stanislav V.
  Multi-threading for Experts Synchronization.
  Technical Report. Intel. 2005. (WWWdocument,
  referenced 17.11.2005). Available
  http//www.intel.com/cd/ids/developer/asmo-na/eng/
  183321.htm

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Question

• Question
• Give a definition and an example for each of
• A symmetric multi-core processor
• An asymmetric multi-core processor
• Answer
• A symmetric multi-core processor is one that has
  multiple cores on a single chip, and all of those
  cores are identical.
• Example Intel Core 2
• An asymmetric multi-core processor is one that
  has multiple cores on a single chip, but those
  cores might be different designs.
• Example Cell Processor.

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