Why Computer Architecture is Exciting and Challenging Daniel

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Why Computer Architecture is Exciting and Challenging Daniel Sorin Department of Electrical & Computer

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,

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

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

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?

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

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

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

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

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

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

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, ? ? ?

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

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.

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

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

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

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

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

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!

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

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

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

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

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

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

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

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

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

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

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