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“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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but first i d like to thank
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
a misconception about what computer architects do
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.”

what would we have done
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
intellectual giant theory
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.

design today more complex

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
multicore
Multicore

$100B industry

Compilers

Apps

Multicore

Vendors

design today scarier
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…
what architects really do
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
recent arch history

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.
system designers todo list
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

products not cpus

$$$

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

power constrained design
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
multicore16
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
reliable systems from unreliable components
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
adjurations
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 