Review of Chapter 1 and exercises

1Copyright © 2012, Elsevier Inc. All rights reserved.

Chapter 1

Fundamentals of Quantitative Design and Analysis

Computer ArchitectureA Quantitative Approach, Fifth Edition


Computer Technology Performance improvements:

Improvements in semiconductor technology Feature size, clock speed

Improvements in computer architectures Enabled by HLL compilers, UNIX Lead to RISC architectures

Together have enabled: Lightweight computers Productivity-based managed/interpreted programming

languages SaaS, Virtualization, Cloud

Applications evolution: Speech, sound, images, video,

“augmented/extended reality”, “big data”

Introduction


Single Processor PerformanceIntroduction

RISC

Move to multi-processor


Current Trends in Architecture Cannot continue to leverage Instruction-Level

parallelism (ILP) Single processor performance improvement ended in

2003

New models for performance: Data-level parallelism (DLP) Thread-level parallelism (TLP) Request-level parallelism (RLP)

These require explicit restructuring of the application

Introduction


Classes of Computers Personal Mobile Device (PMD)

e.g. smart phones, tablet computers (1.8 billion sold 2010) Emphasis on energy efficiency and real-time

Desktop Computing Emphasis on price-performance (0.35 billion)

Servers Emphasis on availability (very costly downtime!), scalability,

throughput (20 million) Clusters / Warehouse Scale Computers

Used for “Software as a Service (SaaS)”, PaaS, IaaS, etc. Emphasis on availability ($6M/hour-downtime at Amazon.com!)

and price-performance (power=80% of TCO!) Sub-class: Supercomputers, emphasis: floating-point

performance and fast internal networks, and big data analytics Embedded Computers (19 billion in 2010)

Emphasis: price

Classes of C

omputers


Parallelism Classes of parallelism in applications:

Data-Level Parallelism (DLP) Task-Level Parallelism (TLP)

Classes of architectural parallelism: Instruction-Level Parallelism (ILP) Vector architectures/Graphic Processor Units (GPUs) Thread-Level Parallelism Request-Level Parallelism

Classes of C

omputers


Flynn’s Taxonomy Single instruction stream, single data stream (SISD)

Single instruction stream, multiple data streams (SIMD) Vector architectures Multimedia extensions Graphics processor units

Multiple instruction streams, single data stream (MISD) No commercial implementation

Multiple instruction streams, multiple data streams (MIMD) Tightly-coupled MIMD Loosely-coupled MIMD

Classes of C

omputers


Defining Computer Architecture “Old” view of computer architecture:

Instruction Set Architecture (ISA) design i.e. decisions regarding:

registers, memory addressing, addressing modes, instruction operands, available operations, control flow instructions, instruction encoding

“Real” computer architecture: Specific requirements of the target machine Design to maximize performance within constraints:

cost, power, and availability Includes ISA, microarchitecture, hardware

Defining C

omputer A

rchitecture


Trends in Technology Integrated circuit technology

Transistor density: 35%/year Die size: 10-20%/year Integration overall: 40-55%/year

DRAM capacity: 25-40%/year (slowing)

Flash capacity: 50-60%/year 15-20X cheaper/bit than DRAM

Magnetic disk technology: 40%/year 15-25X cheaper/bit then Flash 300-500X cheaper/bit than DRAM

Trends in Technology


Bandwidth and Latency Bandwidth or throughput

Total work done in a given time 10,000-25,000X improvement for processors over the

1st milestone 300-1200X improvement for memory and disks over

the 1st milestone

Latency or response time Time between start and completion of an event 30-80X improvement for processors over the 1st

milestone 6-8X improvement for memory and disks over the 1st

milestone



Bandwidth and Latency

Log-log plot of bandwidth and latency milestones



Transistors and Wires Feature size

Minimum size of transistor or wire in x or y dimension

10 microns in 1971 to .032 microns in 2011 Transistor performance scales linearly

Wire delay does not improve with feature size! Integration density scales quadratically Linear performance and quadratic density

growth present a challenge and opportunity, creating the need for computer architect!



Power and Energy Problem: Get power in, get power out

Thermal Design Power (TDP) Characterizes sustained power consumption Used as target for power supply and cooling system Lower than peak power, higher than average power

consumption

Clock rate can be reduced dynamically to limit power consumption

Energy per task is often a better measurement

Trends in Pow

er and Energy


Dynamic Energy and Power Dynamic energy

Transistor switch from 0 -> 1 or 1 -> 0 ½ x Capacitive load x Voltage2

Dynamic power ½ x Capacitive load x Voltage2 x Frequency switched

Reducing clock rate reduces power, not energy

Trends in Pow

er and Energy


Power Intel 80386

consumed ~ 2 W 3.3 GHz Intel

Core i7 consumes 130 W

Heat must be dissipated from 1.5 x 1.5 cm chip

This is the limit of what can be cooled by air

Trends in Pow

er and Energy


Reducing Power Techniques for reducing power:

Do nothing well Dynamic Voltage-Frequency Scaling Low power state for DRAM, disks Overclocking, turning off cores

Trends in Pow

er and Energy


Static Power Static power consumption

Currentstatic x Voltage Scales with number of transistors To reduce: power gating Race-to-halt

The new primary evaluation for design innovation Tasks per joule Performance per watt

Trends in Pow

er and Energy


Trends in Cost Cost driven down by learning curve

Yield

DRAM: price closely tracks cost

Microprocessors: price depends on volume 10% less for each doubling of volume

Trends in Cost


Integrated Circuit Cost Integrated circuit

Bose-Einstein formula: Defects per unit area = 0.016-0.057 defects per square cm (2010) N = process-complexity factor = 11.5-15.5 (40 nm, 2010) The manufacturing process dictates the wafer cost, wafer yield and

defects per unit area The architect’s design affects the die area, which in turn affects the

defects and cost per die

Trends in Cost


Dependability Systems alternate between two states of service

with respect to SLA/SLO:1. Service accomplishment, where service is delivered

as specified by SLA2. Service interruption, where the delivered service is

different from the SLA Module reliability: “failure(F)=transition from 1 to

2” and “repair(R)=transition from 2 to 1” Mean time to failure (MTTF) Mean time to repair (MTTR) Mean time between failures (MTBF) = MTTF + MTTR Availability = MTTF / MTBF

Dependability


Measuring Performance Typical performance metrics:

Response time Throughput

Speedup of X relative to Y Execution timeY / Execution timeX

Execution time Wall clock time: includes all system overheads CPU time: only computation time

Benchmarks Kernels (e.g. matrix multiply) Toy programs (e.g. sorting) Synthetic benchmarks (e.g. Dhrystone) Benchmark suites (e.g. SPEC06fp, TPC-C)

Measuring P

erformance


Principles of Computer Design Take Advantage of Parallelism

e.g. multiple processors, disks, memory banks, pipelining, multiple functional units

Principle of Locality Reuse of data and instructions

Focus on the Common Case Amdahl’s Law

Principles


Principles of Computer Design The Processor Performance Equation

Principles


Principles of Computer DesignP

rinciples

Different instruction types having different CPIs


Chapter 1 Review & Examples

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Instruction Set Architecture (ISA)• Serves as an interface between software and

hardware.• Provides a mechanism by which the software

tells the hardware what should be done.

instruction set

High level language code : C, C++, Java, Fortran,

hardware

Assembly language code: architecture specific statements

Machine language code: architecture specific bit patterns

software

compiler

assembler

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Instruction Set Design Issues

• Instruction set design issues include:– Where are operands stored?

» registers, memory, stack, accumulator– How many explicit operands are there?

» 0, 1, 2, or 3 – How is the operand location specified?

» register, immediate, indirect, . . . – What type & size of operands are supported?

» byte, int, float, double, string, vector. . .– What operations are supported?

» add, sub, mul, move, compare . . .

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Classifying ISAsAccumulator (before 1960, e.g. 68HC11):

1-address add A acc ¬ acc + mem[A]

Stack (1960s to 1970s):0-address add tos ¬ tos + next

Memory-Memory (1970s to 1980s):2-address add A, B mem[A] ¬ mem[A] + mem[B]3-address add A, B, C mem[A] ¬ mem[B] + mem[C]

Register-Memory (1970s to present, e.g. 80x86):2-address add R1, A R1 ¬ R1 + mem[A]

load R1, A R1 ¬ mem[A]

Register-Register (Load/Store, RISC) (1960s to present, e.g. MIPS):3-address add R1, R2, R3 R1 ¬ R2 + R3

load R1, R2 R1 ¬ mem[R2]store R1, R2 mem[R1] ¬ R2

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Operand Locations in Four ISA ClassesGPR

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Code Sequence C = A + B for Four Instruction Sets

Stack Accumulator Register(register-memory)

Register (load-store)

Push APush BAddPop C

Load AAdd BStore C

Load R1, AAdd R1, BStore C, R1

Load R1,ALoad R2, BAdd R3, R1, R2Store C, R3

memory memoryacc = acc + mem[C] R1 = R1 + mem[C] R3 = R1 + R2

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Types of Addressing Modes (VAX)Addressing Mode Example Action

1. Register direct Add R4, R3 R4 <- R4 + R32. Immediate Add R4, #3 R4 <- R4 + 33. Displacement Add R4, 100(R1) R4 <- R4 + M[100 + R1]4. Register indirect Add R4, (R1) R4 <- R4 + M[R1]5. Indexed Add R4, (R1 + R2) R4 <- R4 + M[R1 + R2]6. Direct Add R4, (1000) R4 <- R4 + M[1000]7. Memory Indirect Add R4, @(R3) R4 <- R4 + M[M[R3]]8. AutoincrementAdd R4, (R2)+ R4 <- R4 + M[R2]

R2 <- R2 + d9. Autodecrement Add R4, (R2)- R4 <- R4 + M[R2]

R2 <- R2 - d10. Scaled Add R4, 100(R2)[R3] R4 <- R4 +

M[100 + R2 + R3*d]• Studies by [Clark and Emer] indicate that modes 1-4 account for

93% of all operands on the VAX.

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Types of Operations

• Arithmetic and Logic: AND, ADD• Data Transfer: MOVE, LOAD,

STORE• Control BRANCH, JUMP,

CALL• System OS CALL, VM • Floating Point ADDF, MULF, DIVF• Decimal ADDD, CONVERT• String MOVE, COMPARE• Graphics (DE)COMPRESS

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MIPS Instructions

• All instructions exactly 32 bits wide• Different formats for different purposes• Similarities in formats ease implementation

op rs rt offset

6 bits 5 bits 5 bits 16 bits

op rs rt rd functshamt

6 bits 5 bits 5 bits 5 bits 5 bits 6 bits

R-Format

I-Format

op address

6 bits 26 bits

J-Format

31 0

31 0

31 0

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MIPS Instruction Types

• Arithmetic & Logical - manipulate data in registers

add $s1, $s2, $s3 $s1 = $s2 + $s3or $s3, $s4, $s5 $s3 = $s4 OR $s5

• Data Transfer - move register data to/from memory load & store

lw $s1, 100($s2) $s1 = Memory[$s2 + 100]sw $s1, 100($s2) Memory[$s2 + 100] = $s1

• Branch - alter program flowbeq $s1, $s2, 25 if ($s1==$s1) PC = PC + 4 + 4*25

else PC = PC + 4

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MIPS Arithmetic & Logical Instructions

• Instruction usage (assembly)add dest, src1, src2 dest=src1 + src2sub dest, src1, src2 dest=src1 - src2and dest, src1, src2 dest=src1 AND src2

• Instruction characteristics– Always 3 operands: destination + 2 sources– Operand order is fixed– Operands are always general purpose registers

• Design Principles:– Design Principle 1: Simplicity favors regularity– Design Principle 2: Smaller is faster

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Arithmetic & Logical Instructions - Binary Representation

• Used for arithmetic, logical, shift instructions– op: Basic operation of the instruction (opcode)– rs: first register source operand– rt: second register source operand– rd: register destination operand– shamt: shift amount (more about this later)– funct: function - specific type of operation

• Also called “R-Format” or “R-Type” Instructions



031

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Decimal

Binary

Arithmetic & Logical Instructions -Binary Representation Example

• Machine language for add $8, $17, $18

• See reference card for op, funct values

000000

0

10001

17

10010

18

01000

8

00000

0

100000

32

031

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MIPS Data Transfer Instructions

• Transfer data between registers and memory• Instruction format (assembly)

lw $dest, offset($addr) load wordsw $src, offset($addr) store word

• Uses:– Accessing a variable in main memory– Accessing an array element

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Review: Chapter 1

• Classes of Computers and Classes of Parallelism

• Technology Trend• Dependability• Performance Measurements and Benchmarks• Principles

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5 Classes of Computers

• Personal Mobile Devices– Cost is its primary concern– Energy, media performance, and responsiveness

• Desktop Computing– Price-Performance is its primary concern

• Servers– Availability, Scalability, and Throughput

• Clusters/warehouse-scale computers– Price-Performance, Energy

• Embedded Computer– Price

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Classes of Parallelism & Architectures• Data-Level Parallelism

– Data items can be operated on at the same time• Task-Level Parallelism

– Tasks can operate independently and largely in parallel

• Instruction-Level Parallelism: data-level para.– Pipelining, speculative execution

• Vector Architectures & GPU: data-level para.– A single instruction operates a collection of data in para.

• Thread-Level Parallelism: either data-level para. or task-level para.– Exploits parallelism via parallel threads

• Request-Level Parallelism: task-level para.– Exploits parallelism via decoupled tasks

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4 ways for hardware to support parallelism

• Single Instruction stream, Single Data stream– SISD

• Single Instruction stream, Multiple Data streams– SIMD, e.g., GPU, targets data-level parallelism

• Multiple Instruction streams, Single Data stream– MISD, no commercial multiprocessor of this type

• Multiple Instruction streams, Multiple Data streams– MIMD, e.g., multi-core processors, targets task-level parallelism

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Trend in Technology

• Integrated Circuit (IC) logic technology– Moore’s Law: a growth rate in transistor count on a chip

of about 40%-55% per year, or doubling every 18 or 24 months.

• Semiconductor DRAM– In 2011, a growth rate in capacity: 25%-40% per year

• Flash– A growth rate in capacity: 50%-60% per year

• Magnetic Disk– Since 2004, it has dropped back to 40% per year.

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Trend in Performance

• Bandwidth vs. Latency– The improvement on Bandwidth is much significant than

that on Latency.

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Growth in Processor Performance

RISC

Move to multi-processor

Parallelism: via Pipelining

Locality: using Cache

Hurdle: Power Wall

Lack: Instruction-

level Parallelism

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An example of Intel 486 CPU released in 1992 ， 66MHz, w/ L2 Cache ， 4.9-

6.3W

http://www.cpu-world.com/CPUs/80486/Intel-A80486DX2-66.html

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A CPU fan for Intel 486 CPU

http://www.cnaweb.com/486-ball-bearing-cpu-fan.aspx

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An example of Intel Pentium 4 CPU released in 2002, 2.8GHz, w/ 512KB Cache, 68.4W

http://www.pcplanetsystems.com/abc/product_details.php?item_id=146&category_id=61

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A typical CPU fan for Intel Pentium 4

http://www.dansdata.com/p4coc.htm

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A special CPU fan for gaming/multimedia users

http://www.pcper.com/reviews/Cases-and-Cooling/Asus-Star-Ice-CPU-Cooler-Review

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Trend in Power and Energy in IC

• Energydynamic – ½ X Capacitive Load X Voltage2

• Powerdynamic – ½ X Capacitive Load X Voltage2 X Freq. switched

• Example– Intel 486 66MHz Voltage: 5V– Intel Pentium 4 2.8GHz Voltage: 1.5V– Intel Core 990x 3.4GHz Voltage: 0.8-1.375V

• Improving Energy Efficiency– Do nothing well; Dynamic Voltage-Frequency

Scaling(DVFS); Design for typical case; Overclocking• Powerstatic

– Currentstatic X Voltage

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Dependability

• Service Accomplishment & Service Interruption• Transitions between 2 states: Failure & Restoration• Measurements

– Reliability: a measure of the continuous service accomplishment from a reference initial instant.» MTTF: Mean time to failure» FIT: failures per billion hours, 1/MTTF X 109 » MTTR: Mean time to repair» MTBF: Mean time between failures = MTTF + MTTR

– Availability: a measure of the service accomplishment with respect to the alternation between the two states.» MTTF/(MTTF+MTTR)» Upper bound: 100%

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Performance Measurements and Benchmarks

• Metrics– Throughput: a total amount of work done in a given time– Response time (Execution time): the time between the start and

the completion of an event• Speedup of X relative to Y

– Execution timeY / Execution timeX

• Execution time– Wall clock time: a latency to complete a task– CPU time: only computation time

• Benchmarks– Kernels, Toy programs, Synthetic benchmarks – Benchmark suites: SPEC [CPU] & TPC [Transaction Processing]– SpecRatio = Execution Timereference / Execution Timetarget

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Design Principles

• Take Advantage of Parallelism• Principle of Locality• Focus on the Common Case

– Amdahl’s Law

– Upper bound of the speedup: ?

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Example: Laundry Room

Washing Machine Drying Machine Clean LaundryDirty Laundry

30 minutes washing 90 minutes drying

Total Execution Time: 30+90 = 120 minutesWashing Portion: 30/120 = ¼ Drying Portion: 90/120 = ¾

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If we can have two drying machines

Washing Machine 2 Drying Machines Clean LaundryDirty Laundry

30 minutes washing 90/2=45 minutes drying

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Speedup: (30+90)/(30+45)=1.6

Washing Machine 2 Drying Machines Clean LaundryDirty Laundry

30 minutes washing 90/2=45 minutes drying

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If we can have unlimited drying machines

Washing Machine ∞ Drying Machines Clean LaundryDirty Laundry

30 minutes washing ? minutes drying

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Speedup: (30+90)/(30+0)=4

Washing Machine ∞ Drying Machines Clean LaundryDirty Laundry

30 minutes washing 90/∞ ≈ 0 minutes drying

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Design Principles

• Take Advantage of Parallelism• Principle of Locality• Focus on the Common Case

– Amdahl’s Law

– Upper bound of the speedup: » 1 / (1 - Fractionenhanced)

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Exercise 1

• If the new processor is 10 times faster than the original process, and we assume that the original processor is busy with computation 40% of the time and is waiting for I/O 60% of the time, what is the overall speedup gained by incorporating the enhancement?

• Fractionenhanced = 0.4, Speedupenhanced = 10 • Speedupoverall = 1/(0.6+0.4/10) = 1.56• What is the upper bound of the overall

speedup?• Upper bound = 1/0.6 = 1.67

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Exercise 2

• In a disk subsystem:– 10 disks, each rated at 1,000,000-hour MTTF– 1 ATA controller, 500,000-hour MTTF– 1 power supply, 200,000-hour MTTF– 1 fan, 200,000-hour MTTF– 1 ATA cable, 1,000,000-hour MTTF

• Assuming the lifetimes are exponentially distributed and that failures are independent, compute the MTTF of the system as a whole

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Exercise 2

• Because the overall failure rate of the collection is the sum of the failure rates of the modules, the failure rate of the system– = 10*(1/1,000,000) + 1/500,000 + 1/200,000 + 1/200,000 +

1/1,000,000 – = 23/1,000,000 or 23,000 FIT

• Because MTTF is the inverse of the failure rate– MTTFsystem = 1/(23/1,000,000) = 43,500 hours

Documents

Review of Chapter 1 and exercises