Computer Architecture II 1 Computer architecture II Introduction.
(C) 2002 Daniel SorinDuke Architecture Why Computer Architecture is Exciting and Challenging Daniel...
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Transcript of (C) 2002 Daniel SorinDuke Architecture Why Computer Architecture is Exciting and Challenging Daniel...
(C) 2002 Daniel Sorin Duke Architecture
Why Computer Architecture is Exciting and Challenging
Daniel Sorin
Department of Electrical & Computer Engineering
Duke University
CPS 300 – Daniel Sorinslide 2
Computer Architecture 101
• Computer architects design computer systems– Processors: Intel Pentium 4, IBM PowerPC– Also: memory systems, interconnections, ???
Pentium
cachememory
memory(DRAM) bridge to I/O
diskethernet
card
CPS 300 – Daniel Sorinslide 3
Intro to Microarchitecture (CPS 220 in 1 slide)
• Microarchitects design processors
• Goals for processors:– Faster!!!!– Higher bandwidth communication with memory system– Backward-compatible with previous models
• How do we make processors faster? – Faster clocks (>2 GHz)– Do more work (execute instructions) at same time
CPS 300 – Daniel Sorinslide 4
Intro to Multiprocessor Architecture
• I design computer systems with multiple processors
Node Node Node
InterconnectionNetwork
InterconnectionNetwork
Pentium
cachememory(DRAM) bridge to I/O
diskethernet
card
Node
CPS 300 – Daniel Sorinslide 5
What Multiprocessor Architects Do All Day
• How do we make processors work together?– Exploit parallelism in applications
• Example: web server– Each processor handles different requests– Processors communicate occasionally to synch up
• Some challenges:– Interconnection network design– Protocols for communicating and sharing data– Scalability– Reliability
CPS 300 – Daniel Sorinslide 6
Outline
• What is computer architecture?
• Why is architecture exciting? – Fast-paced: Technology trends– Important: Prevalence of computers
• Why is architecture challenging?
CPS 300 – Daniel Sorinslide 7
Technology Trends – Why do I Care?
• We design an architecture for a given technology• Technology parameters:
– Number of transistors on a chip– Transistor speed– Amount of memory– Memory speed– Bandwidth between components– Power usage– Applications to be run on system
• All of these change dramatically over time!
time
parameter
CPS 300 – Daniel Sorinslide 8
Technology Trends – A Few Examples
• Number of transistors – Doubles every 18 months (Moore’s Law)
• Memory size– 1992: I bought an extra 512Kbytes for my desktop– 2002: My desktop came with 512 Mbytes
• Power usage– Pentium 4 can draw 50 amps of current and burn 50 W
• Important applications– Word processing, spreadsheets multimedia, web surfing
CPS 300 – Daniel Sorinslide 9
Technology Trends – Good or Bad?
• Pessimist: trends make designs obsolete– But now I have to re-think everything I’d already solved!
• Optimist/Architect: trends offer opportunities– What can do we do with a billion transistors?
• Good design ideas Bad design ideas
• E.g., was good idea to scale up processor sizes– But, it now uses too much power and is too complex
CPS 300 – Daniel Sorinslide 10
What To Do With a Billion Transistors?
A. Make the processors bigger
Proc
B. Make more little processors
Proc
chip
chipProc Proc
CPS 300 – Daniel Sorinslide 11
Outline
• What is computer architecture?
• Why is architecture exciting? – Fast-paced: Technology trends– Important: Prevalence of computers
• Why is architecture challenging?
CPS 300 – Daniel Sorinslide 12
Prevalence of Computers
• They’re everywhere!– Desktops, laptops, cars, airplanes, ???
• Optimist/Architect: – More opportunities to innovate!
• Pessimist: we’re in trouble if:– They fail– They use up too much power
Let’s look at these two issues now
CPS 300 – Daniel Sorinslide 13
Computer Availability
• Availability: probability that computer works correctly
• More parts more parts that can fail
• How do we protect computer from failing?– Redundancy (e.g., double bagging your groceries)– Recovery mechanisms (e.g., “Undo” button in PowerPoint)
• My research explores how to detect errors and recover from them
CPS 300 – Daniel Sorinslide 14
Power Usage
• Used to just be a problem for supercomputers– E.g., Cray computers came with coolant system
• Now it’s a problem for all computers (tech trend!)– More computers using more power
CPS 300 – Daniel Sorinslide 15
Outline
• What is computer architecture?
• Why is architecture exciting?
• Why is architecture challenging?– Difficult to evaluate solutions– Inter-related with other fields
CPS 300 – Daniel Sorinslide 16
Ways to Evaluate New Architectures
Simula
ting
Modeling
Building
Tradeoff between three desired features
CPS 300 – Daniel Sorinslide 17
Building
• Construct a hardware prototype
• Advantages+ Way cool to show off hardware to friends+ Runs quickly
• Disadvantages– Takes long time (grad student time!) to build– Expensive– Not flexible
Generally too labor intensive for research studies
CPS 300 – Daniel Sorinslide 18
Modeling
• Mathematically model the system– Use probabilities and/or queuing models
• Advantages+ Very flexible+ Very quick to develop+ Runs quickly
• Disadvantages– Cannot capture effects of system details– Architects are skeptical of models
Generally OK for back of the envelope estimates
mem time = hit time + miss rate*penalty
CPS 300 – Daniel Sorinslide 19
Simulating
• Write a program that mimics system behavior
• Advantages+ Very flexible+ Relatively quick to develop
• Disadvantages– Runs slowly (e.g., 30,000 times slower than hardware)
Method of choice for most architectural research
CPS 300 – Daniel Sorinslide 20
Simulation Challenges
SimulatorApplication
System description
Performance results
Tough problems associated with each arrow!
CPS 300 – Daniel Sorinslide 21
Applications to Simulate
• We care how system does on important applications
• But who defines “important”? (I do!)
• Types of applications– Scientific (genomics, weather simulation, protein folding)– Commercial (database, web serving, application serving)– Desktop (office productivity software, multimedia)– Portable (voice recognition)– ???
CPS 300 – Daniel Sorinslide 22
Describing Simulated System
• How detailed must our simulator be?• Model every transistor in the processor?
– Would take too long
• Abstract away details of processor organization?– Could miss important effects of processor features– Could achieve wrong conclusion
• Need balance– Model in detail only where necessary– E.g., I model memory system in detail, but abstract disks
CPS 300 – Daniel Sorinslide 23
Performance Results
• How do tell if our design is good?• Need metrics for evaluation
• Performance metrics– Clock speed (gigahertz)?– Instructions per cycle?– Database transactions per second
• Compare results to other published research?– Can’t do it!– Major problem in architecture research– JIR = “Journal of Irreproducible Results”
CPS 300 – Daniel Sorinslide 24
Outline
• What is computer architecture?
• Why is architecture exciting?
• Why is architecture challenging?– Difficult to evaluate solutions– Inter-related with other fields
CPS 300 – Daniel Sorinslide 25
Why Architects Need Friends
• Architecture is considered both computer engineering and computer science
• Architects interact with other areas– Circuit design (Electrical Engineering)– Transmission lines (EE)– Power (EE, Mechanical Engineering)– Compilers (Comp Sci)– Operating systems (CS)– Networking (EE, CS)– Databases (CS)– Queuing theory (CS, EE, Industrial Engineering)
CPS 300 – Daniel Sorinslide 26
How Architecture Relates to Other Areas
Computer Architecture
Operating Systems, Compilers, Networking Software
Circuits, Wires, Network Hardware
Application Software
• Besides these interactions, also global issues!
– Power, system verification, performance analysis, etc.
CPS 300 – Daniel Sorinslide 27
How Architecture Relates to Hardware (EE)
Computer Architecture
Operating Systems, Compilers, Networking Software
Circuits, Wires, Network Hardware
Application Software
• Architecture should enable efficient hardware design
– Avoid huge hardware structures
– Avoid cross-chip wires
CPS 300 – Daniel Sorinslide 28
How Architecture Relates to System Software
Computer Architecture
Operating Systems, Compilers, Networking Software
Circuits, Wires, Network Hardware
Application Software
• Architecture should support system software
– Provide good target for compiler (unlike IA-64?)
– Support important OS features (such as synchronization)
CPS 300 – Daniel Sorinslide 29
How Architecture Relates to User Software
Computer Architecture
Operating Systems, Compilers, Networking Software
Circuits, Wires, Network Hardware
Application Software
• Architecture should efficiently run important apps
• Intel added MMX hardware to support media apps
• Sun & IBM design multiprocessors for commercial apps
CPS 300 – Daniel Sorinslide 30
Conclusions
• Computer architecture is way cool, but not easy
• “If it was easy, everyone would do it.” - my Mom
• Students interested in architecture should:– Take ECE 259 / CPS 221 in the spring– Attend architecture/systems seminars in CS department– Take courses in related fields