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What Computer Architects Really Do

“Or should.”. What Computer Architects Really Do. Bob Colwell E-M Talk ISCA ‘05. But First, I’d Like to Thank. Ron Hoelzeman (Pitt), Doug Jensen, Dan Siewiorek (CMU), George Cox, Kevin Kahn Paul Rodman, Dave Papworth, Rich Lethin, Josh Fisher & amazing Multiflow team

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What Computer Architects Really Do

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  1. “Or should.” What Computer Architects Really Do Bob Colwell E-M Talk ISCA ‘05

  2. But First, I’d Like to Thank • Ron Hoelzeman (Pitt), Doug Jensen, Dan Siewiorek (CMU), George Cox, Kevin Kahn • Paul Rodman, Dave Papworth, Rich Lethin, Josh Fisher & amazing Multiflow team • Incredible P6 team, esp. Randy Steck, Glenn Hinton, Mike Fetterman, Andy Glew, Dave Papworth, Gurbir Singh • My parents, Ellen, Kelly, Ken, Kristen • Joe Malingowski • Yale Patt, Wen-mei Hwu, Guri Sohi, Tom Conte, Computer Arch community

  3. Is there a trend here…

  4. A Misconception About What Computer Architects Do EE Times May 23, 2005 “Is the day of the architect over?” “Microprocessor architects managed to re-create almost the whole history of the mainframe computer industry…they used all the tricks, from microprogramming and stripped-down pipelines with load-store architectures to speculative execution and branch prediction. Best of all, hardly anyone was unkind enough to comment that all this ground had been covered already, just at a lesser level of integration.”

  5. What would we have done… Had we been born 300 years ago Same IQ’s but no computers, no electronics Power source = waterwheels and oxen Same brains as today but different challenges Likewise with computer pioneers Issue isn’t “why were they so innovative & why aren’t we” They did what we do: whatever is necessary • Those things change over time

  6. Intellectual Giant Theory Intellectual giants did walk the earth in the ’60’s • Eckert, Mauchly, von N, Conway, Cocke, Brooks, Flynn, Tomasulo… • we should honor pioneering contributions • but today’s designers are not leeches living off that legacy Intellectual giants did walk the earth in the ’60’s. They still do.

  7. system CPU CPU-Mesmerization. Root cause? Profits. Design today: more complex 1960’s complexity • Poor tools, interaction of electronics, packaging & ISA Today’s complexity • Today’s complexity from speed, hyper-aggressive uArch’s, power limits, SW compatibility, number of usage models, CPU-Mesmerization

  8. CPU architect IA32+64-bit exts IA32 64-bit extensions to IA32

  9. Multicore $100B industry Compilers Apps Multicore Vendors

  10. Design today: scarier • No-recalls much harder than design-for-minimal-field-service • Pioneers designed for 1,000 users • Design errors? Charge ‘em for service calls • Today we design for 1,000,000,000 users • Design errors? Pray…

  11. What architects really do • Insidious error: thinking architects design instruction sets & uArch mechanisms • We have, and do, but that misses the point • Architects start out as generals, moonlight as Special Forces • Range freely, identify needs, apply appropriate force • Ensure that biggest risks are attacked first • Make sure project goals are clear & focussed • Seek odd viewing angles to drive out problems • Supply judgment calls where data is lacking • And judgment as to when data should be collected

  12. CPU architects must evolve into system designers Recent arch history • For past two decades an architect’s point of highest leverage has been microarchitecture • Re-use what works • Pipelining, caches, shared buses, superscalar • Invent where necessary • Microdataflow/OOO, trace caches, speculative branch predictors, cache coherency • With some major ISA work on RISCs • But this is changing. Right now.

  13. System Designers todo list “Whatever needs doing” has become… • Products, not CPUs • Power-constrained system design • Multicore (gotta pay the bills, too) • Reliable systems from unreliable components No longer “what I’d like to sell you” but designing what buyers want

  14. $$$ 2004 “killer products” “killer apps” + PC’s iPOD desired delivered Time “PC era” Ubiq. comp. Products Not CPUs Cell phones Ray tracing Portable computing “Speed at any price” “What’s in it for me?” -buyer

  15. Power-constrained design • “fast as possible at max power” will yield to “fast enough, no faster” • Lesson from the embedded space • Thermal variability vs. guaranteed real-time • Throw in wireless links for good measure • Battery life, not just cooling cost • Global warming, energy crisis looms • It ain’t just cars and oil prices • Be synchronized to public taste or lose

  16. Multicore • “Here I come, ready or not…” • We can build ‘em. Can we… • Compile to them? • Feed them? (bandwidth) • Cool them? (power) • Write apps for them? • Clear and present challenge • There are pots of gold associated w/ this

  17. Reliable Systems from Unreliable Components • N-mod redundancy too expensive • Transient errors, manufacturing defects, design errors • Must survive them all • Solution can’t drive power up • Still want guaranteed performance for real-time • Intel’s Shekhar Borkar says we have at most 10 years to figure this out

  18. Adjurations • Computer revolution is only getting started • Role of architects is changing • If we don’t do it who will? • Your grandchildren will thank you • And wonder if they’re as smart as you were 

  19. backups

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