CpE442 Lec2.1 Introduction to Computer Architectures
CpE 442Introduction to Computer Architecture
The Role of Performance
Instructor: H. H. Ammar
CpE442 Lec2.2 Introduction to Computer Architectures
Overview of Today’s Lecture: The Role of Performance
° Review from Last Lecture
° Definition and Measures of Performance
° Benchmarks
° Summarizing Performance and Performance Pitfalls
CpE442 Lec2.3 Introduction to Computer Architectures
Review: What is "Computer Architecture"
° Co-ordination of levels of abstraction
I/O systemInstr. Set Proc.
Compiler
OperatingSystem
Application
Digital Design
Circuit Design
° Under a set of rapidly changing Forces
Instruction SetArchitecture
CpE442 Lec2.4 Introduction to Computer Architectures
Review: Levels of Representation
High Level Language Program
Assembly Language Program
Machine Language Program
Control Signal Specification
Compiler
Assembler
Machine Interpretation
temp = v[k];
v[k] = v[k+1];
v[k+1] = temp;
lw $15, 0($2)
lw $16, 4($2)
sw $16, 0($2)sw $15, 4($2)
0000 1001 1100 0110 1010 1111 0101 1000
1010 1111 0101 1000 0000 1001 1100 0110
1100 0110 1010 1111 0101 1000 0000 1001
0101 1000 0000 1001 1100 0110 1010 1111
CpE442 Lec2.5 Introduction to Computer Architectures
Review: Levels of Organization
SPARCstation 20
SPARCProcessor
Computer
Control
Datapath
Memory Devices
Input
Output
CpE442 Lec2.6 Introduction to Computer Architectures
1. The HASE Architecture Simulation Environment
2. The New Compiler Technology simulation (shown in class)
3. MIPS Assembly Language Simulatorsa. SPIM A MIPS32 Simulatorhttp://pages.cs.wisc.edu/~larus/spim.html
b. MARS (MIPS Assembler and Runtime Simulator)http://courses.missouristate.edu/kenvollmar/mars/
Computer Architecture Simulation Tools
CpE442 Lec2.7 Introduction to Computer Architectures
Review: Summary from Last Lecture
° All computers consist of five components
• Processor: (1) datapath and (2) control
• (3) Memory
• (4) Input devices and (5) Output devices
° Not all “memory” are created equally
• Cache: fast (expensive) memory are placed closer to the processor
• Main memory: less expensive memory--we can have more
° Input and output (I/O) devices has the messiest organization
• Wide range of speed: graphics vs. keyboard
• Wide range of requirements: speed, standard, cost ... etc.
• Least amount of research (so far)
CpE442 Lec2.8 Introduction to Computer Architectures
Overview of Today’s Lecture: The Role of Performance
° Review from Last Lecture
° Definition and Measures of Performance
° Benchmarks
° Summarizing Performance and Performance Pitfalls
CpE442 Lec2.9 Introduction to Computer Architectures
Metrics of performance
Compiler
Programming
Language
Application
Datapath
Control
Transistors Wires Pins
ISA
Function Units
(millions) of Instructions per second – MIPS
(millions) of (F.P.) operations per second – MFLOP/s
Cycles per second (clock rate)
Megabytes per second
Response time, Answers per month
Operations per second
CpE442 Lec2.10 Introduction to Computer Architectures
Relating Processor Metricsthe execution time of a given program on a given CPU architecture
° CPU execution time = CPU clock cycles/pgm X clock cycle time
° or CPU execution time = CPU clock cycles/pgm ÷ clock rate
° Define CPI = the avg. clock cycles per instruction, CPI tells us something about the Instruction Set Architecture, the Implementation of that architecture, and the program being measured
° CPU clock cycles/pgm = Instructions/pgm X CPI
° or CPI = CPU clock cycles/pgm ÷ Instructions/pgm
CpE442 Lec2.11 Introduction to Computer Architectures
Aspects of CPU Performance,
CPU time = Seconds = Instructions x Cycles x Seconds
Program Program Instruction Cycle
instr. count CPI clock rate
Program
Compiler
Instr. Set Arch.
Organization
Technology
CpE442 Lec2.12 Introduction to Computer Architectures
Aspects of CPU Performance
CPU time = Seconds = Instructions x Cycles x Seconds
Program Program Instruction Cycle
instr count CPI clock rate
Program X (x)
Compiler X (x)
Instr. Set. X X
Organization X X
Technology X
CpE442 Lec2.13 Introduction to Computer Architectures
Figures from a Simulator for the following code segment comparing two compilers
for (i=0;i<3;i++) { in_a(i)++; int_b(i)++; flt_d(i) = flt_d(i) + flt_c(i); }
CpE442 Lec2.14 Introduction to Computer Architectures
CpE442 Lec2.15 Introduction to Computer Architectures
CpE442 Lec2.16 Introduction to Computer Architectures
CpE442 Lec2.17 Introduction to Computer Architectures
CpE442 Lec2.18 Introduction to Computer Architectures
Organizational Trade-offs
Compiler
Programming
Language
Application
Datapath
Control
Transistors Wires Pins
ISA
Function Units
Instruction Mix
Cycle Time
CPISingle-Cycle Processor Design
CPI=1, large cycle time-Slow clock
Multi-cycle Processor Design
CPI > 1, smaller cycle time- Faster
clock
CpE442 Lec2.19 Introduction to Computer Architectures
CPI
CPU time = ClockCycleTime * S CPI * Ii = 1
n
i i
CPI = S CPI * F where F = I
i = 1
n
i i i i
Instruction Count
"instruction frequency"
Invest Resources where time is Spent!
CPI = (CPU Time * Clock Rate) / Instruction Count
= Clock Cycles / Instruction Count
“Average cycles per instruction”
The performance equation can be written as follows using instruction classes
and the instruction count I and CPI for each class i
See example next slide
CpE442 Lec2.20 Introduction to Computer Architectures
Example
Typical Mix
Base Machine (Reg / Reg)
Op Freq(Fi) CPI(i) % Time
ALU 50% 1 .5 33%
Load 20% 2 .4 27%
Store 10% 2 .2 13%
Branch 20% 2 .4 27%
1.5
The CPI = 1.5 cycles per instruction
CpE442 Lec2.21 Introduction to Computer Architectures
Enhanced Machine (Reg / Reg)
Op Freq CPI(i) % Time
ALU 50% 1 .5 25%
Load 20% 3 .6 30%
Store 10% 3 .3 15%
Branch20% 3 .6 30%
2.0
Assume a program of 1 million instructions, Compare the
performance of
Base Machine (B) with the above CPI, 1 GHZ clock, and
Enhanced Machine (E) with 1.333 GHZ and a one cycle increase
for L/S and branch instructions
CpE442 Lec2.22 Introduction to Computer Architectures
Comparing the performance of two machines
Speedup due to enhancement E:
ExTime w/o E Performance w/ E
Speedup(E) = -------------------- = ---------------------
ExTime w/ E Performance w/o E
= Perf. of E / Perf. of B = exec. Time of B /
exec. Time of E
= 1.5 * 1 / 2 * 0.75 = 1
Performance of B is similar to that of E,
No gain in performance
CpE442 Lec2.23 Introduction to Computer Architectures
Rate Metrics – MIPS (Million Instructions Per Second), and
MFLPOS (Miilions Floating Point Operations Per Second)
MIPS = Instruction Count / (CPU Time * 10^6)
= Clock Rate / (CPI * 10^6)
•machines with different instruction sets ?
•programs with different instruction mixes ?
dynamic frequency of instructions
• uncorrelated with performance
MFLOP/S= FP Operations / (Time * 10^6)
•machine dependent
•often not where time is spent
CpE442 Lec2.24 Introduction to Computer Architectures
Example showing why MIPS can failCompare performance with Compilers 1 and 2 for a given program on a given machine
Instruction Count in Billions forinstruction classes A B C
Compiler 1 Instruction Count 5 1 1Compiler 2 Instruction Count 10 1 1CPI for each class 1 2 3
Clock cycles using compiler1 = 10 BillionClock cycles using compiler2 = 15 Billion
assuming 1GHZ clockCPU Time 1 = 5x1+1x2 +1x3 = 10 secsCPU Time 2 = 10x1 + 1x2 + 1x3 = 15 secs
yet the MIPS rating isMIPS 1 = (instr. Count/cpu time in sec x 10^6)
= (5+1+1)/10 * 1000 = 700MIPS 2 = 12/15 * 1000 = 800giving the impression that 2 have a higher rate of executing instructions than 1
CpE442 Lec2.25 Introduction to Computer Architectures
Overview of Today’s Lecture: The Role of Performance
° Review from Last Lecture
° Definition and Measures of Performance
° Benchmarks
° Summarizing Performance and Performance Pitfalls
CpE442 Lec2.26 Introduction to Computer Architectures
Why Do Benchmarks?
° How we evaluate differences
• Different systems
• Changes to a single system
° Provide a target
• Benchmarks should represent large class of important programs
• Improving benchmark performance should help many programs
° For better or worse, benchmarks shape a field
° Good ones accelerate progress
• good target for development
° Bad benchmarks hurt progress
• help real programs v. sell machines/papers?
• Inventions that help real programs don’t help benchmark
CpE442 Lec2.27 Introduction to Computer Architectures
Programs to Evaluate Processor Performance
° (Toy) Benchmarks
• 10-100 line
• e.g.,: sieve, puzzle, quicksort
° Synthetic Benchmarks
• attempt to match average frequencies of real workloads
• e.g., Whetstone, dhrystone
° Kernels
• Time critical excerpts Real programs
• e.g., gcc, spice
CpE442 Lec2.28 Introduction to Computer Architectures
Successful Benchmark: SPEChttp://www.spec.org/benchmarks.html
http://mrob.com/pub/comp/benchmarks/spec.html#CPU_06
° EE Times + 5 companies band together to form the Systems Performance Evaluation Committee (SPEC): Sun, MIPS, HP, Apollo, DEC
° Create standard list of programs, inputs, reporting: some real programs, includes OS calls, some I/O
CpE442 Lec2.29 Introduction to Computer Architectures
SPEC second round, SPEC95
• 8 integer benchmarks in C and 10 floating pt benchmarks in Fortran
CpE442 Lec2.30 Introduction to Computer Architectures
CpE442 Lec2.31 Introduction to Computer Architectures
CpE442 Lec2.32 Introduction to Computer Architectures
Overview of Today’s Lecture: The Role of Performance
° Review from Last Lecture
° Definition and Measures of Performance
° Benchmarks
° Summarizing Performance and Performance Pitfalls
CpE442 Lec2.33 Introduction to Computer Architectures
Amdahl's Law
Speedup due to enhancement E:
ExTime w/o E Performance w/ E
Speedup(E) = -------------------- = ---------------------
ExTime w/ E Performance w/o E
Suppose that enhancement E accelerates a fraction F of the task
by a factor S and the remainder of the task is unaffected then,
ExTime(with E) = ((1-F) + F/S) X ExTime(without E)
Speedup(with E) = ExTime(without E) ÷((1-F) + F/S) X ExTime(without E)
<= 1/(1-F) speed up is bounded by this factor
CpE442 Lec2.34 Introduction to Computer Architectures
Performance Evaluation Summary
° Time is the measure of computer performance!
° Good products created when have:
• Good benchmarks
• Good ways to summarize performance
° If not good benchmarks and summary, then choice between improving product for real programs vs. improving product to get more sales=> sales almost always wins
° Remember Amdahl’s Law: Speedup is limited by unimproved part of programs
° HW 1, Submit via ecampus
CPU time = Seconds = Instructions x Cycles x Seconds
Program Program Instruction Cycle