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Multi-Core Computing

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Title: Multi-Core Computing


1
Multi-Core Computing
  • Ahmad Aljebaly
  • Department of Computer Science
  • Western Michigan University

2
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

3
Introduction
  • First Microprocessor(1970s)
  • Intel 4004
  • PC spreads in the world(1980s)
  • Up to 32bits microprocessor
  • AMD followed Intels technology

4
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

5
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

6
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.

7
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.

8
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.

9
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.

10
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.

11
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.

12
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)

13
Multi-core architectures
  • Replicate multiple processor cores on a single
    die.
  • The cores fit on a single processor socket.

14
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
15
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

16
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.

17
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.

18
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

19
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

20
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.

21
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.

22
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.

23
Symmetric Multi-core Processor
All cores which exist in a die are exactly
identical
24
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.

25
Symmetric Multi-core Processor
  • Applications
  • Personal Computers
  • Server / Super Computer

26
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.

27
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.

28
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.
29
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.

30
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.

31
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.

32
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.

33
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.

34
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)

35
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 .

36
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

37
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.

38
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.

39
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.

40
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

41
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.

42
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