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  1. VLSI and Computer Architecture Trends ECE 25 Fall 2012

  2. A Brief History • 1958: First integrated circuit • Flip-flop using two transistors • From Texas Instruments • 2011 • Intel 10 Core Xeon Westmere-EX • 2.6 billion transistors • 32 nm process Courtesy Texas Instruments Courtesy Intel

  3. Moore’s Law • Historical growth rate • 2x transistors & clock speeds every 2 years over 50 years • 10x every 6-7 years • Dramatically more complex algorithms previously not feasible • Dramatically more realistic video games and graphics animation (e.g. Playstation 4, Xbox 360 Kinect, Nintendo Wii) • 1 Mb/s DSL to 10 Mb/s Cable to 2.4 Gb/s Fiber to Homes • 2G to 3G to 4G wireless communications • MPEG-1 to MPEG-2 to MPEG-4 to H.264 video compression • 480 x 270 (0.13 million pixels) NTSC to 1920x1080 (2 million pixels) HDTV resolution to 2880x1800 (5 million pixels) Retina Display

  4. Standard Cells NOR-3 XOR-2

  5. Standard Cell Layout

  6. NVIDIA GeForce 8800(600+ million transistors, about 60+ million gates)

  7. NVIDIA Kepler2 GK104 GPU(1536 cores, 3.54 billion transistors)

  8. Subwavelength Lithography Challenges Source: Raul Camposano, 2003

  9. NRE Mask Costs Source: MIT Lincoln Labs, M. Fritze, October 2002

  10. ASIC NRE Costs Not Justified for Many Applications • A complex ASIC will have an NRE Cost of over $40M = $28M (NRE Design Cost) + $12M (NRE Mask Cost) • Many “ASIC” applications will not have the volume to justify a $40M NRE cost • e.g. a $30 IC with a 33% margin would require sales of 4M units (x $10 profit/IC) just to recoup $40M NRE Cost

  11. Power Density a Key Issue • Motivated mainly by power limits • Ptotal = Pdynamic + Pleakage • Pdynamic = ½ a C VDD2 f • Problem: power (heat dissipation) density has been growing exponentially because clock frequency (f) and transistor count have been doubling every 2 years

  12. Power Density a Key Issue • Had scaling continued at previous pace, by 2005, high speed processors would have power density of nuclear reactor by 2005, a rocket nozzle by 2010, and would become the power density of the sun’s by 2015. Courtesy: Intel

  13. e.g. Intel Itanium II 6-Way Integer Unit < 2% die area Cache logic > 50% die area Most of chip there to keep these 6 Integer Units at “peak” rate Main issue is external DRAM latency (50ns) to internal clock (0.25ns) is 200:1 Increase performance by higher clock frequency and more complex pipelining & speculative execution Before Multicore Processors INT6 Cache logic

  14. Multicore Era • Multicore era • Operate at lower voltage and lower clock frequency • Simpler processor cores • Increase performance by more cores per chip • e.g. Intel 10 Core Xeon Westmere-EX • 1.73-2.66 GHz (vs. previous Xeonsat 4 Ghz) 1 core

  15. Embedded Multicore Processors • Embedded multicore processors replacing ASICs • Much simpler processor cores, much smaller caches • e.g. Tilera-GX: 100 processors

  16. What Does the Future Look Like? Corollary of Moore’s law: Number of cores will double every 18 months ‘05 ‘08 ‘11 ‘14 ‘02 Research 64 256 1024 4096 16 Industry 16 64 256 1024 4 Source: MIT, A. Agrawal, 2009

  17. ITRS Roadmap • Semiconductor Industry Association forecast • Intl. Technology Roadmap for Semiconductors

  18. Power Revisited • Ptotal = Pdynamic + Pleakage • Pdynamic = ½ a C VDD2 f • Historically, Pleakage was negligible, Pdynamicdominated. • Power could be controlled by reducing VDD (which used to be 5V, now about 1V). • Lowering VDD requires lowering threshold voltage, but Pleakage becomes more dominant, which is why we are not reducing VDD much any more, or very slowly.

  19. Classical scaling Device count S2 Device frequency S Device power (cap) 1/S Device power (VDD) 1/S2 Utilization 1 Leakage limited scaling Device count S2 Device frequency S Device power (cap) 1/S Device power (VDD) ~1 Utilization 1/S2 Scaling theory S = Exponentially increasing problem! The Utilization Wall(Source: S. Swanson, M. Taylor 2010)

  20. Age of “Dark Silicon”(Source: S. Swanson, M. Taylor 2010) • Spectrum of tradeoffs • between # cores and • frequency. • e.g.; take • 65 nm32 nm; • i.e. (s =2) 2x4 cores @ 3 GHz (8 cores dark) (Industry’s Choice) .… 4 cores @ 3 GHz .… 4 cores @ 2x3 GHz (12 cores dark) 32 nm 65 nm

  21. Moving Back to Specialized Silicon? Dark Silicon • “Traditional” Operating System • Provide many “modules” in software that“applications” call at run-time. • OS modules only “loaded” in memory when used. • Most OS modules unused at any moment. • Moving OS into silicon? • Power more expensive than area. • Specialized logic can improve energy efficiency 10-1000x. • Possible idea: move power-intensive OS modules into silicon or build specialized hardware accelerators. • Most of these “silicon modules” would be “dark”: only “lite-up” when called. • In another words, “waste” silicon to save power. Source: S. Swanson, M. Taylor, GreenDroid Project, 2010

  22. Questions?