lecture 5 - multiprocessors

7/24/2019 Lecture 5 - Multiprocessors

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MultiprocessorsCOMP 211 – Computer Systems Organization and Architecture

ACL 201302!



"ntroduction

As their name suggest, multiprocessor systemsutilizes more than one processor to improveperformance.

Early multiprocessor systems used multiple

processor to improve throughput by executingindependent jobs on different processors.



"ntroduction

Dividing a single program’s wor among multipleprocessors, multiprocessors can achieve greaterperformance than is possible with a singleprocessor in any given fabrication technology.

!he terms multitasing or multiprogramming aremore appropriate to describe this concept, which isimplemented mostly in software, whereasmultiprocessing is more appropriate to describe the

use of multiple hardware "#$s. A system can beboth multiprocessing and multiprogramming, onlyone of the two, or neither of the two of them.



VS



Multi core

a single computing component with two or moreindependent actual central processing units %called&cores&', which are the units that read and executeprogram instructions.



Multiprocessor

(t is a tightly coupled computer systemhaving two or more processing units %MultipleProcessors' each sharing main memory andperipherals, in order to simultaneously process

programs.



Designer of uniprocessor systems, measureperformance in terms of speedup.

)imilarly, multiprocessor architects measureperformance in terms of speedup.

Microprocessors Speedup



Microprocessors Speedup



Linear Speedup!he execution time of program on an n*

processor system would be 1/nth of the executiontime on a one*processor system

Super Linear Speedup(t occurs when programs are sometimes more

efficient on multiprocessor systems than onuniprocessor systems.

"deal Microprocessors Speedup



(nterprocessor communication

)ynchronization

+oad alancing

Limitations o# Speedup



"nterprocessor communication

-henever one processor generates %computes' avalue that is needed by the fraction of the programrunning on another processor, that value must be

communicated to the processors that need it, whichtaes time

n a uniprocessor system, the entire program

runs on one processor, so there is no timelost to interprocessor communication




Synchronization

(t is often necessary to synchronize the processorsto ensure that they have all completed some phaseof the program before any processor begins woring

on the next phase of the program.




Load $alancing

(n many parallel applications, it is difficult to dividethe program across the processors such that eachprocessor’s chun of the wor tae the same amount

of time.

)ome of the processor’s completes their tas earlyand are idle waiting for the others to finish.

This results in increasing the overallexecution time.




/ultiprocessors consist of processors connectedby a communications networ.

Multiprocessor Systems

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0etwor



ASS"%&'

A()hat is multithreading*

Ad+antage and disad+antage$( %i+en ,ypes O# Multiprocessors' -t.ocolumns/

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"entralized /emory )ystem

Distributed /emory )ystem

,ypes o# Multiprocessors



!here is only one memory system for the entire

multiprocessor, and memory references from all ofthe processors go to that memory system.

Centralized Memory System

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0etwor

/emory



Advantages:

All data in the memory is accessible by allprocessors!here will never be a problem with multiplecopies of a given datum.

(t is a better design when the number ofprocessors in the system is small.A single memory may be able to meet thebandwidth demands of the processors.

Disadvantage:!he bandwidth does not increase as thenumber of processors increase.

Centralized Memory System



Each processor has its own memory system,

which it can access directly. (n obtaining the datathat is stored in some other processor’s memory, aprocessor must communicate with it to re1uest thedata.

istri7uted Memory System

0etwor

/emory /emory /emory /emory

"#$ "#$ "#$ "#$

"#$ "#$ "#$ "#$

/emory /emory /emory /emory



Advantages:

Each processor has its own memory system. !here is more total bandwidth in the memorysystem than in a centralized memory system, andthat the latency to complete a memory re1uest is

lower. $sed when the latency of the networ isunacceptably long enough for the "/) to handle.

Disadvantage: nly some of the data in the memoryis directly accessible by each processor, since aprocessor can only read and write itslocal memory system.

istri7uted Memory System



(t is structured as a set of communicating

processes, with no shared mutable state.

(t can involve rendezvous between sender andreceiver.

Synchronous – Sender waits for receiver Asynchronous – Sender continues immediately

after sending a message

(t allows easy system upgrade

Message8Passing Systems



(t can provide a single address space that all of

the processors can read and write.

!he communications happen is implicit.

!he memory system handles inter*processorcommunication by allowing all processors tosee data written by any processor.

Shared8Memory Systems



Defines when memory operations executed on one

processor become visible on other processors.

!wo "onsistency /odels )trong "onsistency

* dictates that the memory system act exactlyas if there were only one memory in the computerthat different processors tae turns using.

2elaxed "onsistency* allowing different processors to have different

values for a given datum until the program re1ueststhat all memories made consistent.

Memory Consistency Models



(t defines how data can be shared and replicated

across processors.

(t also defines the specific set of actions that areexecuted to eep each processor’s view of memory

system consistent.

Cache Coherence



Advantage: /emory references can actually complete faster

if some other processors has a copy of the re1uiredline

Disadvantage: !he bandwidth available over the bus does not

grow as the number of processors in the systemincreases.



$us87ased Shared8Memory System

Processor

Cache

Processor

Cache

Processor

Cache

Processor

Cache

MA"& MMO9

Memory $us Memory $us



ASSIGNMENT:

WHAT IS SISD, MISD, SIMD, MIMD (PROVIDE

ILLUSTRATION

lecture 5 - multiprocessors

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