Computer Technology Performance Metrics
CS 154: Computer Architecture Lecture #3
Winter 2020
Ziad Matni, Ph.D.
Dept. of Computer Science, UCSB
Administrative
Lab 01 how did Friday go?
Gradescope account?
Piazza account?
Remember: due date is Wednesday on Gradescope!
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Job/Help Opportunity
Disabled Students Program Notetaker Needed
CMPSC 154 MW 12:30
$25 per unit (of the class)
(prorated based on the number of weeks for which they are selected)
Questions can be sent to DSP Notetaking Email: [email protected]
Potential Notetakers can apply online at http://dsp.sa.ucsb.edu/services
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Lecture Outline
Tech Details Trends
Historical context
The manufacturing process of ICs
Important Performance Measures CPU time
CPI
Other factors (power, multiprocessors) Pitfalls
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Single-Thread Processor Performance
[ Hennessy & Patterson, 2017 ]
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Computing Devices for General Purposes
Charles Babbage (UK)
Analytical Engine could calculate polynomial
functions and differentials
Inspired by older generation of calculating machines made by Blaise Pascal (1623-1662, France)
Calculated results, but also
stored intermediate findings
(i.e. precursor to computer memory)
Father of Computer Engineering Ada Byron Lovelace (UK)
Worked with Babbage and foresaw computers doing much more than calculating numbers
Loops and Conditional Branching
Mother of Computer Programming 1/13/20
C. Babbage (1791
1871)
A. Byron Lovelace (1815
1852)
Part of Babbages Analytical Engine
Images from Wikimedia.org
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The Modern Digital Computer
Calculating machines kept being produced in the early 20th century (IBM was established in the US in 1911)
Instructions were very simple, which made hardware implementation easier, but this hindered the creation of complex programs.
Alan Turing (UK)
Theorized the possibility of computing machines capable of performing any conceivable mathematical computation as long as this was representable as an algorithm
Called Turing Machines (1936) ideas live on today
Lead the effort to create a machine to successfully decipher the
German Enigma Code during World War II
A. Turing (1912
1954)
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Zuse Z3 (1941)
Built by Konrad Zuse in wartime Germany using 2000 relays
Could do floating-point arithmetic with hardware
22-bit word length ; clock frequency of about 45 Hz!!
64 words of memory!!!
Two-stage pipeline
1) fetch & execute, 2) writeback
No conditional branch
Programmed via paper tape
Replica of the Zuse Z3 in the Deutsches Museum, Munich
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[Venusianer, Creative Commons BY-SA 3.0 ]
ENIAC (1946)
First electronic general-purpose computer
Constructed during WWII to calculate firing tables for US Army Trajectories (for bombs) computed in 30 seconds instead of 40 hours Was very fast for its time started to replace human computers
Used vacuum tubes (transistors hadnt been invented yet)
Weighed 30 tons, occupied 1800 sq ft
It used 160 kW of power (about 3000 light bulbs worth)
It cost $6.3 million in todays money to build.
Programmed by plugboard and switches, time consuming!
As a result of large number of tubes, it was often broken
(5 days was longest time between failures!)
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ENIAC
Changing the program could take days!
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[Public Domain, US Army Photo]
Comparing todays cell phones (with dual CPUs), with ENIAC, we see they
cost 17,000X less
are 40,000,000X smaller use 400,000X less power are 120,000X lighter AND
are 1,300X more powerful.
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EDVAC (1951)
ENIAC team started discussing stored-program concept to speed up programming and simplify machine design
Based on ideas by John von Nuemann & Herman Goldstine Still the basis for our general CPU architecture today
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Commercial computers:
BINAC (1949) and UNIVAC (1951) at EMC
Eckert and Mauchly left academia and formed the Eckert- Mauchly Computer Corporation (EMC)
Worlds first commercial computer was BINAC which didnt work
Second commercial computer was UNIVAC
Famously used to predict presidential election in 1952 Eventually 46 units sold at >$1M each
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IBM 650 (1953)
The first mass-produced computer
Low-end system aimed at businesses rather than scientific enterprises
Almost 2,000 produced
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[Cushing Memorial Library and Archives, Texas A&M, Creative Commons Attribution 2.0 Generic ]
Improvements in C.A.
IBM 650s instruction set architecture (ISA)
44 instructions in base instruction set, expandable to 97 instructions
Hiding instruction set completely from programmer using the concept of high-level languages like Fortran (1956), ALGOL (1958) and COBOL (1959)
Allowed the use of stack architecture, nested loops, recursive calls, interrupt handling, etc
Adm. Grace Hopper (1906 1992), inventor of several High-level language concepts
1/13/20 Matni, CS154, Wi20 [Public Domain, wikimedia] 15
Manufacturing ICs
Yield: the proportion of working dies per wafer; often expressed as a number between 0 and 1
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Example: Intel Core i7 Wafer
300mm (diameter) wafer
280 chips
Each chip is 20.7 mm x 10.5 mm
32nm CMOS technology
(the size of the smallest piece of logic
and the type of Silicon semiconductor used)
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Costs of Manufacturing ICs
Wafer cost and area are fixed
Defect rate determined by manufacturing process
Die area determined by architecture and circuit design
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Examples
A 300 mm wafer of silicon has 500 die on it, of which 100 are not working or malfunctioning. What is the yield of this wafer?
Y = Ngood/Ntotal = 400/500 = 80%
If the wafer costs $200, what is the cost per die?
Cost per die = ($200)/(500 * 0.8) = $200/400 = $0.50
A 300 mm wafer of silicon has N dies that are 0.5 mm x 1 mm each.
What is N?
Area of wafer/Area of each die
= (p * (300/2 * 10-3)2) / (0.5 * 1 * 10-6) = 141,370.605
So, N = 141,370 (round down)
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Response Time and Throughput
Response time (aka Latency)
How long it takes to do a fixed task
Throughput
Total work done per a fixed time
e.g., tasks/transactions/ per hour
How are response time and throughput affected by Replacing the processor with a faster version?
Adding more processors?
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Latency vs. Throughput
Which is more important?
They are different.
It depends on what your goals are Scientific program? Latency
Web server? Throughput
Example: Move people 10 miles
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Via car: Via bus:
Latency:
Throughput:
capacity = 5, speed = 60 mph capacity = 60, speed = 20 mph
car = 10 minutes, bus = 30 minutes
car = 15 PPH, bus = 60 PPH (consider round-trips)
Performance Measures
Execution Time: Total response time, including EVERYTHING CPU time (processing), I/O use, OS overhead, any idle time
This determines system performance
CPU time:
Time spent just processing a given job
(discounts I/O time, OS time, etc) CPU time = user CPU time + system CPU time
Define Performance = 1/Execution Time Relative performance
The performance of system A vs performance of system B, ie. PA / PB 1/13/20 Matni, CS154, Wi20 22
CPU Clocking
Most digital hardware today operates to a constant-rate clock Clock period: duration of a clock cycle
e.g.250ps=0.25ns=2501012s
Clock frequency: clock rate or cycles per second
e.g.4.0GHz=4000MHz=4.0x109Hz Hertz (Hz) is cycles per second, so
clock freq. = 1 / clock period
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Useful Prefixes (Multipliers) to Know
Prefix
Symbol
Multiplier
In words
Scientific Notation
Kilo
k
1,000
thousand
103
Mega
M
1,000,000
million
106
Giga
G
1,000,000,000
billion
109
Tera
T
1,000,000,000,000
trillion
1012
Peta
P
1,000,000,000,000,000
quadrillion
1015
Prefix
Symbol
Multiplier
In words
Scientific Notation
milli
m
0.001
thousandth
10-3
micro
0.000001
millionth
10-6
nano
n
0.000000001
billionth
10-9
pico
p
0.000000000001
trillionth
10-12
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CPU Time
Performance can be improved (i.e. make CPU Time less) by
Reducing number of clock cycles
Increasing clock rate
Hardware designer must often trade off clock rate against cycle count
Example: it took the CPU 1000 cycles to run the program. The clock cycle time (i.e. period) is 10 ns, so the CPU time is: 1000x10ns=10000ns=10s,or10x10-6 s
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Instruction Count and CPI
Instruction Count for a program
Determined by program, ISA and compiler
Average cycles per instruction (CPI)
Determined by CPU hardware
If different instructions have different CPI, then Average CPI is affected by instruction mix
Example: next slide
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CPI Example
Computer A: Cycle Time = 250 ps, CPI = 2.0 Computer B: Cycle Time = 500 ps, CPI = 1.2 Same Instruction Set Architecture (ISA)
Which is faster?
CPU Time = Instruction Count x CPI x Cycle Time
CPU_Time_A=NIx2.0x250x10-12 s=NIx500x10-12 s CPU_Time_B=NIx1.2x500x10-12 s=NIx600x10-12 s So, CPU A is faster than CPU B
By how much is it faster?
RelativePerformance=NIx600x10-12 s/NIx500x10-12 s=1.2
So, CPU A is 1.2 times faster than B (or you could say its 20% faster)
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CPI Example using Weighted Classes
An instruction class = instruction type
e.g. arithmetic type vs. branching type vs. jump type, etc
A CPU compiles code sequences using instructions in classes A, B, C
Sequence1:IC=5,soClockCycles=21+12+23=10 So, Avg. CPI = 10/5 = 2.0
Sequence2:IC=6,soClockCycles=41+12+13=9 So,Avg.CPI=9/6=1.5
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Other Factors to CPU Performance:
Power Consumption
Market trends DEMAND that power consumption of CPUs keep decreasing.
Power and Performance DONT always go together
Power = Capacitive Load x Voltage2 x Clock Frequency So:
Decreasing Voltage helps to get lower power, but it can make individual logic go slower!
Increasing clock frequency helps performance, but increases power! Its a dilemma that has contributed to Moores Law plateau
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YOUR TO-DOs for the Week
BRING YOUR MIPS REF CARDS TO CLASS!!! Do your reading for next class (see syllabus)
Finish up Assignment #1 for lab (lab01)
You have to submit it as a PDF using Gradescope Due on Wednesday, 1/15, by 11:59:59 PM
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