Why Computer Architecture is Exciting and Challenging Daniel
- Slides: 30
Why Computer Architecture is Exciting and Challenging Daniel Sorin Department of Electrical & Computer Engineering Duke University (C) 2002 Daniel Sorin Duke Architecture
Computer Architecture 101 • Computer architects design computer systems – Processors: Intel Pentium 4, IBM Power. PC – Also: memory systems, interconnections, ? ? ? Pentium cache memory 2 disk memory (DRAM) ethernet card bridge to I/O CPS 300 – Daniel Sorin
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 3 CPS 300 – Daniel Sorin
Intro to Multiprocessor Architecture • I design computer systems with multiple processors Node Pentium disk cache memory (DRAM) ethernet card bridge to I/O Interconnection Network 4 CPS 300 – Daniel Sorin
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: – – 5 Interconnection network design Protocols for communicating and sharing data Scalability Reliability CPS 300 – Daniel Sorin
Outline • What is computer architecture? • Why is architecture exciting? – Fast-paced: Technology trends – Important: Prevalence of computers • Why is architecture challenging? 6 CPS 300 – Daniel Sorin
Technology Trends – Why do I Care? • We design an architecture for a given technology • Technology parameters: parameter – – – – Number of transistors on a chip Transistor speed Amount of memory Memory speed Bandwidth between components Power usage Applications to be run on system time • All of these change dramatically over time! 7 CPS 300 – Daniel Sorin
Technology Trends – A Few Examples • Number of transistors – Doubles every 18 months (Moore’s Law) • Memory size – 1992: I bought an extra 512 Kbytes 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 8 CPS 300 – Daniel Sorin
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 9 CPS 300 – Daniel Sorin
What To Do With a Billion Transistors? A. Make the processors bigger Proc chip B. Make more little processors Proc 10 chip CPS 300 – Daniel Sorin
Outline • What is computer architecture? • Why is architecture exciting? – Fast-paced: Technology trends – Important: Prevalence of computers • Why is architecture challenging? 11 CPS 300 – Daniel Sorin
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 12 CPS 300 – Daniel Sorin
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 Power. Point) • My research explores how to detect errors and recover from them 13 CPS 300 – Daniel Sorin
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 14 CPS 300 – Daniel Sorin
Outline • What is computer architecture? • Why is architecture exciting? • Why is architecture challenging? – Difficult to evaluate solutions – Inter-related with other fields 15 CPS 300 – Daniel Sorin
Ways to Evaluate New Architectures Tradeoff between three desired features M od g it n a l u eli n g im S Building 16 CPS 300 – Daniel Sorin
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 17 CPS 300 – Daniel Sorin
Modeling • Mathematically model the system – Use probabilities and/or queuing models • Advantages mem time = hit time + miss rate*penalty + 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 18 CPS 300 – Daniel Sorin
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 19 CPS 300 – Daniel Sorin
Simulation Challenges Application Simulator Performance results System description Tough problems associated with each arrow! 20 CPS 300 – Daniel Sorin
Applications to Simulate • We care how system does on important applications • But who defines “important”? (I do!) • Types of applications – – – 21 Scientific (genomics, weather simulation, protein folding) Commercial (database, web serving, application serving) Desktop (office productivity software, multimedia) Portable (voice recognition) ? ? ? CPS 300 – Daniel Sorin
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 22 CPS 300 – Daniel Sorin
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” 23 CPS 300 – Daniel Sorin
Outline • What is computer architecture? • Why is architecture exciting? • Why is architecture challenging? – Difficult to evaluate solutions – Inter-related with other fields 24 CPS 300 – Daniel Sorin
Why Architects Need Friends • Architecture is considered both computer engineering and computer science • Architects interact with other areas – – – – 25 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 Sorin
How Architecture Relates to Other Areas Application Software Operating Systems, Compilers, Networking Software Computer Architecture Circuits, Wires, Network Hardware • Besides these interactions, also global issues! – Power, system verification, performance analysis, etc. 26 CPS 300 – Daniel Sorin
How Architecture Relates to Hardware (EE) Application Software Operating Systems, Compilers, Networking Software Computer Architecture Circuits, Wires, Network Hardware • Architecture should enable efficient hardware design – Avoid huge hardware structures – Avoid cross-chip wires 27 CPS 300 – Daniel Sorin
How Architecture Relates to System Software Application Software Operating Systems, Compilers, Networking Software Computer Architecture Circuits, Wires, Network Hardware • Architecture should support system software – Provide good target for compiler (unlike IA-64? ) – Support important OS features (such as synchronization) 28 CPS 300 – Daniel Sorin
How Architecture Relates to User Software Application Software Operating Systems, Compilers, Networking Software Computer Architecture Circuits, Wires, Network Hardware • Architecture should efficiently run important apps • Intel added MMX hardware to support media apps • Sun & IBM design multiprocessors for commercial apps 29 CPS 300 – Daniel Sorin
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 30 CPS 300 – Daniel Sorin
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