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Pertemuan 23Reduced Instruction Set Computer 1

Matakuliah : H0344/Organisasi dan Arsitektur Komputer

Tahun : 2005

Versi : 1/1

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Learning Outcomes

Pada akhir pertemuan ini, diharapkan mahasiswa

akan mampu :

• Menjelaskan prinsip kerja Reduced Instruction Set Computer

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Outline Materi

• Instruction Execution Characteristics

• The Use of Large Register File

• Compiler-Based Register Optimization

• Reduced Instruction Set Architecture

• RISC Pipelining

• RISC versus CISC Controversy

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Overview

Key element of RISC:

1. A large number of general purpose registers, and/or the use of compiler technology to optimize register usage.

2. A limited and simple instruction set.

3. An emphasis on optimizing the instruction pipeline.

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CISC RISC Superscalar

CharacteristicIBM

370/168VAX

11/780Intel

80486SPARC

MIPS R4000

PowerPCUltra

SPARCMIPS

R1000

Year developed 1973 1978 1989 1987 1991 1993 1996 1996

Number of instructions

208 303 235 69 94 225

Instruction size (byte)

2-6 2-57 1-11 4 4 4 4 4

Addressing modes 4 22 11 1 1 2 1 1

Number of general purpose registers

16 16 8 40-520 32 32 40-520 32

Control memory size (kbits)

420 480 246 - - - - -

Cache size (kbyte) 64 64 8 32 128 16-32 32 64

Overview

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Instruction Execution Characteristics

The major cost in the life cycle of system is software, not hardware.

Researchers and industry have been to develop ever more powerful and complex high level programming languages. These high level language (HLLs) allow the programmer to express algorithms more concisely, take care more detail, and often support naturally the use of structured programming or object oriented design.

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Instruction Execution Characteristics

Operations performed

Study language workload

[HUCH83] [KNUT71] [PATT82] [TANE78]

Pascal Scientific

Fortran Student

Pascal SystemC

SystemSal

System

Assign 74 67 45 38 42

Loop 4 3 5 3 4

Call 1 3 15 12 12

If 20 11 29 43 36

Goto 2 9 - 3 -

Other - 7 6 1 6

Relative dynamic frequency of high level language operations

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Instruction Execution Characteristics

Operations performed

%Dynamic Occurrence

Machine instruction weighted

Memory reference weighted

Pascal C Pascal C Pascal C

Assign 45 38 13 13 14 15

Loop 5 3 42 32 33 26

Call 15 12 31 33 44 45

If 29 43 11 21 7 13

Goto - 3 - - - -

Other 6 1 3 1 2 1

Weighted relative dynamic frequency of HLL operation

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Instruction Execution Characteristics

Operands used

Dynamic percentage of operands

% Pascal C Average

Integer constant 16 23 20

Scalar variable 58 53 55

Array/structure 26 24 25

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Instruction Execution Characteristics

Procedure calls

Procedure arguments and local scalar variables

Percentage of executed procedure calls with

Compiler, interpreter, and

typesetter

Small nonnumeric program

>3 arguments 0-7 0-5

>5 arguments 0-3 0

>8 words of arguments and local scalars

1-20 0-6

>12 word of arguments and local scalar

1-6 0-3

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Instruction Execution Characteristics

Implication

1. Use a large number of registers or use a compiler to optimize register usage.

2. Careful attention need to be paid to the design of instruction pipelines.

3. A simplified (reduced) instruction set is indicated.

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The use of a large register file

The most accesses are to local scalars.

1. The software approach is to rely on compiler to maximize register usage.

2. The hardware approach is simply to use more register so that more variables can be held in registers for longer periods of time.

A strategy is needed that will allow the most frequently accessed operands to be kept in registers and to minimize register-memory operations.

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The use of a large register file

Register windows

1. A typical procedure employs only a few passed parameters and local variable

2. The depth of procedure activation fluctuates within a relative narrow range.

The facts:

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The use of a large register file

Register windows

Overlapping register windows

Parameterregisters

Localregisters

Temporaryregisters

Parameterregisters

Localregisters

Temporaryregisters

Call/return

Level J

Level J + 1

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B.in

B.loc

C.in

D.in

C.loc

D.loc

A.in

A.loc

(F)

(E)

w0 w1

w2

w3w4

w5

Savewindowspointer

Currentwindowspointer

SaveRestore

Return

Call

The use of a large register file

Register windows

Circular buffer organization of overlapped windows

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The use of a large register file

Large register file versus cache

Characteristics of large register file and cache organizations

Large register file Cache

All local scalars Recently used local scalars

Individual variables Blocks of memory

Compiler assigned global variables Recently used global variables

Save/restore based on procedure nesting depth

Save/restore based on cache replacement algorithm

Register addressing Memory addressing

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The use of a large register file

Large register file versus cache

Referencing a scalar

R

DecoderW#

Registers

Data

Instruction

A

Instruction

Tags Data

Compare Select

(a) Windows based register file (b) Cache

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A B C D E F

DE

R1 R2 R3

A

D F

B

C E

(b) Register interference graph(a) Time sequence of active use of registers

Compiler based register optimization

Graph coloring approach