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Parallel and Multiprocessor Architectures. Chapter 9.4. By Eric Neto. Parallel & Multiprocessor Architecture. In making processors faster, we run into certain limitations. Physical Economic Solution: When necessary, use more processors, working in sync.

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parallel multiprocessor architecture
Parallel & Multiprocessor Architecture
  • In making processors faster, we run into certain limitations.
    • Physical
    • Economic
  • Solution: When necessary, use more processors, working in sync.
parallel multiprocessor limitations
Parallel & Multiprocessor Limitations
  • Though parallel processing can speed up performance, the amount is limited.
  • Intuitively, you’d expect N processors to do the work in 1/N time, but processes sometimes work in sequences, so there will be some downtime while dormant processors wait for the active processor to finish.
  • Therefore, the more sequential a process is, the less cost-effective it is to implement parallelism.
parallel and multiprocessing architectures
Parallel and Multiprocessing Architectures
  • Superscalar
  • VLIW
  • Vector
  • Interconnection Networks
  • Shared Memory
  • Distributed Computing
superscalar architecture
Superscalar Architecture
  • Allow multiple instructions to be executed simultaneously in each cycle.
  • Contain
    • Execution units – Each allows for one process to execute.
    • Specialized instruction fetch unit – Fetch multiple instructions at once, send them to decoding unit.
    • Decoding unit – Determines whether the given instructions are independent of one another.
vliw architecture
VLIW Architecture
  • Similar to superscalar, but relies on compiler rather than specific hardware.
  • Puts independent instructions into one “Very Long Instruction Words”
  • Advantages:
    • More simple hardware
  • Disadvantages:
    • Instructions fixed at compile time, so some modifications could affect execution of instructions
vector processors
Vector Processors
  • Use vector pipelines to store and perform operations on many values at once, as opposed to Scalar processing, which only performs operations on individual values.
  • Since it uses fewer instructions, there is less decoding, control unit overhead, and memory bandwidth usage.
  • Can be SIMD or MIMD.

LDV V1, R1

LDV V2, R2

ADDV R3, V1, V2

STV R3, V3

Xn= X1 + X2 ;

Yn= Y1 + Y2 ;

Zn= Z1 + Z2 ;

Wn= W1 + W2 ;


interconnection networks
Interconnection Networks
  • Each processor has it’s own memory, that can be accessed and shared by other processors through an interconnected network.
  • Efficiency of messages shared through the network is limited based on:
    • Bandwidth
    • Message latency
    • Transport latency
    • Overhead
  • In general, the amount of messages sent and distances they must travel are minimized.
  • Connections between networks can be either static or dynamic.
  • Different configurations of static processors are more useful for different tasks.

Completely Connected



more topologies
More Topologies




dynamic networks
Dynamic Networks
  • Busses, Crossbars, Switches, Multistage connections.
  • As you implement more processors, these get exponentially more expensive.
dynamic networking crossbar network
Dynamic Networking:Crossbar Network
  • Efficient
  • Direct
  • Expensive
dynamic networking switch network
Dynamic Networking:Switch Network
  • Complex
  • Moderately Efficient
  • Cheaper
dynamic networking bus
Dynamic Networking:Bus
  • Simple
  • Slow
  • Inefficient
  • Cheap
shared memory multiprocessors
Shared Memory Multiprocessors
  • Memory is shared either globally or locally, or a combination of the two.
shared memory access
Shared Memory Access
  • Uniform Memory Access systems use a shared memory pool, where all memory takes the same amount of time to access.
    • Quickly becomes expensive when more processors are added.
shared memory access1
Shared Memory Access
  • Non-Uniform Memory Access systems have memory distributed across all the processors, and it takes less time for a processor to read from its own local memory than from non-local memory.
    • Prone to cache coherence problems, which occur when a local cache isn’t in sync with non-local caches representing the same data.
    • Dealing with these problems require extra mechanisms to ensure coherence.
distributed computing
Distributed Computing
  • Multi-Computer processing
  • Works on the same principal as multi-processors on a larger scale.
  • Uses a large network of computers to solve small parts of a very large problem.