cis775: computer architecture
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CIS775: Computer Architecture. Chapter 1: Fundamentals of Computer Design. Course Objectives. To evaluate the issues involved in choosing and designing instruction set. To learn concepts behind advanced pipelining techniques. - PowerPoint PPT PresentationTRANSCRIPT
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CIS775: Computer Architecture
Chapter 1: Fundamentals of Computer Design
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Course Objectives
• To evaluate the issues involved in choosing and designing instruction set.
• To learn concepts behind advanced pipelining techniques.
• To understand the “hitting the memory wall” problem and the current state-of-art in memory system design.
• To understand the qualitative and quantitative tradeoffs in the design of modern computer systems
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What is Computer Architecture?
• Functional operation of the individual HW units within a computer system, and the flow of information and control among them.
TechnologyProgrammingLanguageInterface
Interface Design(ISA)
Measurement & Evaluation
Parallelism
Computer Architecture:
Applications OS
Hardware Organization
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Computer Architecture Topics
Instruction Set Architecture
Pipelining, Hazard Resolution,Superscalar, Reordering, Prediction, Speculation,Vector, DSP
Addressing,Protection,Exception Handling
L1 Cache
L2 Cache
DRAM
Disks, WORM, Tape
Coherence,Bandwidth,Latency
Emerging TechnologiesInterleaving Memories
RAID
VLSI
Input/Output and Storage
MemoryHierarchy
Pipelining and Instruction Level Parallelism
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Computer Architecture Topics
M
Interconnection NetworkS
PMPMPMP° ° °
Topologies,Routing,Bandwidth,Latency,Reliability
Network Interfaces
Shared Memory,Message Passing,Data Parallelism
Processor-Memory-Switch
MultiprocessorsNetworks and Interconnections
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Measurement and Evaluation
Design
Analysis
Architecture is an iterative process:• Searching the space of possible designs• At all levels of computer systems
Creativity
Good IdeasGood Ideas
Mediocre IdeasBad Ideas
Cost /PerformanceAnalysis
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Issues for a Computer Designer• Functional Requirements Analysis (Target)
– Scientific Computing – HiPerf floating pt.– Business – transactional support/decimal arith.– General Purpose –balanced performance for a range of tasks
• Level of software compatibility– PL level
• Flexible, Need new compiler, portability an issue
– Binary level (x86 architecture)• Little flexibility, Portability requirements minimal
• OS requirements– Address space issues, memory management, protection
• Conformance to Standards– Languages, OS, Networks, I/O, IEEE floating pt.
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Computer Systems: Technology Trends
• 1988– Supercomputers
– Massively Parallel Processors
– Mini-supercomputers
– Minicomputers
– Workstations
– PC’s
• 2002– Powerful PC’s and
SMP Workstations
– Network of SMP Workstations
– Mainframes
– Supercomputers
– Embedded Computers
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Why Such Change in 10 years?• Performance
– Technology Advances• CMOS (complementary metal oxide semiconductor) VLSI dominates older
technologies like TTL (transistor transistor logic) in cost AND performance
– Computer architecture advances improves low-end • RISC, pipelining, superscalar, RAID, …
• Price: Lower costs due to …– Simpler development
• CMOS VLSI: smaller systems, fewer components
– Higher volumes– Lower margins by class of computer, due to fewer services
• Function :Rise of networking/local interconnection technology
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Growth in Microprocessor Performance
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Six Generations of DRAMs
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Updated Technology Trends(Summary)
Capacity Speed (latency)
Logic 4x in 4 years 2x in 3 years
DRAM 4x in 3 years 2x in 10 years
Disk 4x in 2 years 2x in 10 years
Network (bandwidth) 10x in 5 years
• Updates during your study period??
BS (4 yrs)
MS (2 yrs)
PhD (5 yrs)
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Cost of Microprocessors
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DAP.S98 1
IC cost = Die cost + Testing cost + Packaging cost
Final test yield
Die cost = Wafer cost
Dies per Wafer * Die yield
Dies per wafer = š * ( Wafer_diam / 2)2 – š * Wafer_diam – Test dies
Die Area ¦ 2 * Die Area
Die Yield = Wafer yield * 1 +Defects_per_unit_area * Die_Area
Integrated Circuits Costs
Die Cost goes roughly with die area4
{
}
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Performance Trends(Summary)
• Workstation performance (measured in Spec Marks) improves roughly 50% per year (2X every 18 months)
• Improvement in cost performance estimated at 70% per year
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Computer Engineering Methodology
Evaluate ExistingEvaluate ExistingSystems for Systems for BottlenecksBottlenecks
Simulate NewSimulate NewDesigns andDesigns and
OrganizationsOrganizations
Implement NextImplement NextGeneration SystemGeneration System
TechnologyTrends
Benchmarks
Workloads
ImplementationComplexity
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How to Quantify Performance?
• Time to run the task (ExTime)– Execution time, response time, latency
• Tasks per day, hour, week, sec, ns … (Performance)– Throughput, bandwidth
Plane
Boeing 747
BAD/Sud Concodre
Speed
610 mph
1350 mph
DC to Paris
6.5 hours
3 hours
Passengers
470
132
Throughput (pmph)
286,700
178,200
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The Bottom Line: Performance and Cost or Cost
and Performance?"X is n times faster than Y" means
ExTime(Y) Performance(X)
--------- = ---------------ExTime(X) Performance(Y)
• Speed of Concorde vs. Boeing 747
• Throughput of Boeing 747 vs. Concorde
• Cost is also an important parameter in the equation which is why concordes are being put to pasture!
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Measurement Tools
• Benchmarks, Traces, Mixes• Hardware: Cost, delay, area, power estimation• Simulation (many levels)
– ISA, RT, Gate, Circuit
• Queuing Theory• Rules of Thumb• Fundamental “Laws”/Principles• Understanding the limitations of any
measurement tool is crucial.
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Metrics of Performance
Compiler
Programming Language
Application
DatapathControl
Transistors Wires Pins
ISA
Function Units
(millions) of Instructions per second: MIPS(millions) of (FP) operations per second: MFLOP/s
Cycles per second (clock rate)
Megabytes per second
Answers per monthOperations per second
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Cases of Benchmark Engineering• The motivation is to tune the system to the benchmark to achieve peak
performance.• At the architecture level
– Specialized instructions
• At the compiler level (compiler flags)– Blocking in Spec89 factor of 9 speedup– Incorrect compiler optimizations/reordering.– Would work fine on benchmark but not on other programs
• I/O level– Spec92 spreadsheet program (sp)– Companies noticed that the produced output was always out put to a file (so they stored
the results in a memory buffer) and then expunged at the end (which was not measured).– One company eliminated the I/O all together.
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After putting in a blazing performance on the benchmark test, Sun issued a glowing press release claiming that it hadoutperformed Windows NT systems on the test. Pendragon president Ivan Phillips cried foul, saying the resultsweren't representative of real-world Java performance and that Sun had gone so far as to duplicate the test's code within Sun'sJust-In-Time compiler. That's cheating, says Phillips, who claims that benchmark tests and real-world applications aren'tthe same thing.
Did Sun issue a denial or a mea culpa? Initially, Sun neither denied optimizing for the benchmark test nor apologized forit. "If the test results are not representative of real-world Java applications, then that's a problem with the benchmark,"Sun's Brian Croll said.
After taking a beating in the press, though, Sun retreated and issued an apology for the optimization.[Excerpted from PC Online 1997]
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Issues with Benchmark Engineering
• Motivated by the bottom dollar, good performance on classic suites more customers, better sales.
• Benchmark Engineering Limits the longevity of benchmark suites
• Technology and Applications Limits the longevity of benchmark suites.
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SPEC: System Performance Evaluation Cooperative
• First Round 1989– 10 programs yielding a single number (“SPECmarks”)
• Second Round 1992– SPECInt92 (6 integer programs) and SPECfp92 (14 floating point
programs)• Compiler Flags unlimited. March 93 • new set of programs: SPECint95 (8 integer programs) and SPECfp95 (10
floating point)
– “benchmarks useful for 3 years”– Single flag setting for all programs: SPECint_base95,
SPECfp_base95 – SPEC CPU2000 (11 integer benchmarks – CINT2000, and 14
floating-point benchmarks – CFP2000
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SPEC 2000 (CINT 2000)Results
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SPEC 2000 (CFP 2000)Results
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Reporting Performance Results
• Reproducability Apply them on publicly available
benchmarks. Pecking/Picking order– Real Programs– Real Kernels– Toy Benchmarks– Synthetic Benchmarks
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How to Summarize Performance
• Arithmetic mean (weighted arithmetic mean) tracks execution time: sum(Ti)/n or sum(Wi*Ti)
• Harmonic mean (weighted harmonic mean) of rates (e.g., MFLOPS) tracks execution time: n/sum(1/Ri) or 1/sum(Wi/Ri)
• Normalized execution time is handy for scaling performance (e.g., X times faster than SPARCstation 10)
• But do not take the arithmetic mean of normalized execution time, use the geometric mean = (Product(Ri)^1/n)
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Performance Evaluation• “For better or worse, benchmarks shape a field”• Good products created when have:
– Good benchmarks– Good ways to summarize performance
• Given sales is a function in part of performance relative to competition, investment in improving product as reported by performance summary
• If benchmarks/summary inadequate, then choose between improving product for real programs vs. improving product to get more sales;Sales almost always wins!
• Execution time is the measure of computer performance!
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Simulations
• When are simulations useful?
• What are its limitations, I.e. what real world phenomenon does it not account for?
• The larger the simulation trace, the less tractable the post-processing analysis.
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Queueing Theory
• What are the distributions of arrival rates and values for other parameters?
• Are they realistic?
• What happens when the parameters or distributions are changed?
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Quantitative Principles of Computer Design
• Make the Common Case Fast– Amdahl’s Law
• CPU Performance Equation– Clock cycle time– CPI– Instruction Count
• Principles of Locality• Take advantage of Parallelism
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DAP.S98 32
Amdahl's LawSpeedup 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
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Amdahl’s Law
ExTimenew = ExTimeold x (1 - Fractionenhanced) + Fractionenhanced
Speedupoverall =ExTimeold
ExTimenew
Speedupenhanced
=
1
(1 - Fractionenhanced) + Fractionenhanced
Speedupenhanced
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Amdahl’s Law
• Floating point instructions improved to run 2X; but only 10% of actual instructions are FP
Speedupoverall =
ExTimenew =
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CPU Performance EquationCPU time = Seconds = Instructions x Cycles x
Seconds
Program Program Instruction Cycle
CPU time = Seconds = Instructions x Cycles x Seconds
Program Program Instruction Cycle
Inst Count CPI Clock RateProgram X
Compiler X (X)
Inst. Set. X X
Organization X X
Technology X
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Cycles Per Instruction
CPU time = CycleTime * CPI * Ii = 1
n
i i
CPI = 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 = Cycles / Instruction Count
“Average Cycles per Instruction”
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Example: Calculating CPI
Typical Mix
Base Machine (Reg / Reg)
Op Freq Cycles 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
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Chapter Summary, #1• Designing to Last through Trends
Capacity Speed
Logic 2x in 3 years 2x in 3 years
DRAM 4x in 3 years 2x in 10 years
Disk 4x in 3 years 2x in 10 years
• 6yrs to graduate => 16X CPU speed, DRAM/Disk size
• Time to run the task– Execution time, response time, latency
• Tasks per day, hour, week, sec, ns, …– Throughput, bandwidth
• “X is n times faster than Y” means ExTime(Y) Performance(X)
--------- = --------------
ExTime(X) Performance(Y)
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Chapter Summary, #2
• Amdahl’s Law:
• CPI Law:
• Execution time is the REAL measure of computer performance!
• Good products created when have:– Good benchmarks, good ways to summarize performance
• Die Cost goes roughly with die area4
Speedupoverall =ExTimeold
ExTimenew
=
1
(1 - Fractionenhanced) + Fractionenhanced
Speedupenhanced
CPU time = Seconds = Instructions x Cycles x Seconds
Program Program Instruction Cycle
CPU time = Seconds = Instructions x Cycles x Seconds
Program Program Instruction Cycle
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Food for thought
• Two companies reports results on two benchmarks one on a Fortran benchmark suite and the other on a C++ benchmark suite.
• Company A’s product outperforms Company B’s on the Fortran suite, the reverse holds true for the C++ suite. Assume the performance differences are similar in both cases.
• Do you have enough information to compare the two products. What information will you need?
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Food for Thought II• In the CISC vs. RISC debate a key argument of the
RISC movement was that because of its simplicity, RISC would always remain ahead.
• If there were enough transistors to implement a CISC on chip, then those same transistors could implement a pipelined RISC
• If there was enough to allow for a pipelined CISC there would be enough to have an on-chip cache for RISC. And so on.
• After 20 years of this debate what do you think?• Hint: Think of commercial PC’s, Moore’s law and
some of the data in the first chapter of the book (and on these slides)
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Amdahl’s Law (answer)
• Floating point instructions improved to run 2X; but only 10% of actual instructions are FP
Speedupoverall = 1
0.95= 1.053
ExTimenew = ExTimeold x (0.9 + .1/2) = 0.95 x ExTimeold