Multiprocessors

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Multiprocessors

• ELEC 6200 Computer Architecture and Design
• Instructor Agrawal
• Name Nam

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Why we have to use multiprocessors?

• Definition Multiprocessors are parallel
  processors with a single shared address.
• Multiprocessors have the highest performance , it
  is higher than the fastest uni-processor.
• Multiprocessors have a lot of more effective
  applications than a uni-processor search
  engines, web servers, databases.
• Multitasking within an application

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Instruction and data stream of Multiprocessors.

• SIMD (single instruction, multiple data) every
  unit will be executing the same instruction, each
  execution unit has its own address registers, and
  so each unit can have different data addresses.
• MIMD ( multiple instructions, multiple data)
  Machines using MIMD have a number of processors
  that function asynchronously and independently.
  At any time, different processors may be
  executing different instructions on different
  pieces of data
• MISD

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How multiprocessors work?

• How do parallel processors share data?
• How do parallel processors coordinate?
• How many processors?
• Multiprocessors communicate through shared
  variables in memory , all processors can access
  any memory location via loads and stores
• As processors operating in parallel, they
  normally share data. Only one processor at a

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• time can acquire the lock and other
  processors interested in shared data have to wait
  until the original processor unlocks the variable
  so called Lock approach.
• Or processors can communicate by sending and
  receiving message.
• Parallel processing program to refer to a single
  program that runs on multiple processors
  simultaneously
• it is difficult to write parallel processing
  programs, the programmer must know a good deal
  about the hardware.

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Multiprocessors connected by a single bus
Processors
Processors
Processors
Cashes
Cashes
Cashes
Single Bus
Memory
I/O
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• Each microprocessor is much smaller than a
  multichip processor, so more processors can be
  placed on a bus.
• Caches can lower bus traffic.
• Mechanisms were invented to keep caches and
  memory consistent for multiprocessors
• Traffic per processor and the bus bandwidth
  determine the useful number of processors in such
  a multiprocessor.
• Single bus designs are attractive but limited
  high bandwidth, low latency, and long length,
• Limit to the bandwidth of a single memory
  module as well----gt limited number of processors

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Multiprocessors connected by a network
Processors
Processors
Processors
Cashes
Cashes
Cashes
Memory
Memory
Memory
Network
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• In machines without a single global address
  space, communication is explicit the programmer
  or the compiler must send messages to ship data
  to another node and must receive messages to
  accept data from another node.
• Send and receive also have the advantage of
  making it easier for the programmer to optimize
  communication its simpler to overlap
  computation with communication by using explicit
  sends and receives rather than with implicit
  loads and stores.

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New tendency

• An alternative to multiple microprocessors
  sharing an interconnect is bringing the
  processors inside the chip. In such designs, the
  processors typically share some of the caches and
  the external memory interface.
• Advantage amortize the instruction accesses, the
  latencies associated with chip-to-chip
  communication disappear ,Shared data structures
  are also much less of a problem
• Challenge lies in software. What architecture
  makes software easier.

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Thank You