What Computer What Computer Architects Architects Really DoReally Do

Bob ColwellBob ColwellE-M Talk ISCA ‘05E-M Talk ISCA ‘05

“Or should.”“Or should.”

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But First, I’d Like to ThankBut First, I’d Like to Thank

Ron Hoelzeman (Pitt), Doug Jensen, Dan Ron Hoelzeman (Pitt), Doug Jensen, Dan Siewiorek (CMU), George Cox, Kevin Kahn Siewiorek (CMU), George Cox, Kevin Kahn

Paul Rodman, Dave Papworth, Rich Lethin, Paul Rodman, Dave Papworth, Rich Lethin, Josh Fisher & amazing Multiflow teamJosh Fisher & amazing Multiflow team

Incredible P6 team, esp. Randy Steck, Glenn Incredible P6 team, esp. Randy Steck, Glenn Hinton, Mike Fetterman, Andy Glew, Dave Hinton, Mike Fetterman, Andy Glew, Dave Papworth, Gurbir SinghPapworth, Gurbir Singh

My parents, Ellen, Kelly, Ken, KristenMy parents, Ellen, Kelly, Ken, KristenJoe MalingowskiJoe MalingowskiYale Patt, Wen-mei Hwu, Guri Sohi, Tom Yale Patt, Wen-mei Hwu, Guri Sohi, Tom

Conte, Computer Arch communityConte, Computer Arch community

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Is there a trend here…Is there a trend here…

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A Misconception About What A Misconception About What Computer Architects DoComputer Architects DoEE Times May 23, 2005EE Times May 23, 2005

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

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What would we have done…What would we have done…

Had we been born 300 years agoHad we been born 300 years agoSame IQ’s but no computers, no electronicsSame IQ’s but no computers, no electronics

Power source = waterwheels and oxenPower source = waterwheels and oxen

Same brains as today but different challengesSame brains as today but different challenges

Likewise with computer pioneersLikewise with computer pioneersIssue isn’t “why were they so innovative & why Issue isn’t “why were they so innovative & why

aren’t we”aren’t we”

They did what we do: whatever is necessaryThey did what we do: whatever is necessaryThose things change over timeThose things change over time

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Intellectual Giant TheoryIntellectual Giant Theory

Intellectual giants did walk the earth in Intellectual giants did walk the earth in the ’60’sthe ’60’s– Eckert, Mauchly, von N, Conway, Cocke, Brooks, Eckert, Mauchly, von N, Conway, Cocke, Brooks,

Flynn, Tomasulo…Flynn, Tomasulo…– we should honor pioneering contributionswe should honor pioneering contributions– but today’s designers are not leeches living off but today’s designers are not leeches living off

that legacythat legacy

Intellectual giants did walk the earth in Intellectual giants did walk the earth in the ’60’s. the ’60’s. They still doThey still do..

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Design today: more complexDesign today: more complex

1960’s complexity1960’s complexity– Poor tools, interaction of Poor tools, interaction of

electronics, packaging & ISAelectronics, packaging & ISA

Today’s complexityToday’s complexity– Today’s complexity from speed, Today’s complexity from speed,

hyper-aggressive uArch’s, power hyper-aggressive uArch’s, power limits, SW compatibility, number of limits, SW compatibility, number of usage models, usage models, CPU-MesmerizationCPU-Mesmerization

CPU

system

CPU-Mesmerization. Root cause? Profits.

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IA32+64-bit exts IA32

CPU architect

64-bit extensions to IA3264-bit extensions to IA32

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MulticoreMulticore

Com

pile

rsA

pps Multicore

Vendors

$100B industry

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Design today: scarierDesign today: scarier

No-recalls much harder than design-No-recalls much harder than design-for-minimal-field-servicefor-minimal-field-service– Pioneers designed for 1,000 usersPioneers designed for 1,000 users

Design errors? Charge ‘em for service callsDesign errors? Charge ‘em for service calls

– Today we design for 1,000,000,000 usersToday we design for 1,000,000,000 usersDesign errors? Pray…Design errors? Pray…

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What architects really doWhat architects really do

Insidious error: thinking architects design Insidious error: thinking architects design instruction sets & uArch mechanismsinstruction sets & uArch mechanisms

We have, and do, but that misses the pointWe have, and do, but that misses the point– Architects start out as generals, moonlight as Special Architects start out as generals, moonlight as Special

ForcesForces

– Range freely, identify needs, apply appropriate forceRange freely, identify needs, apply appropriate force

– Ensure that biggest risks are attacked firstEnsure that biggest risks are attacked first

– Make sure project goals are clear & focussedMake sure project goals are clear & focussed

– Seek odd viewing angles to drive out problemsSeek odd viewing angles to drive out problems

– Supply judgment calls where data is lackingSupply judgment calls where data is lacking

And judgment as to when data should be And judgment as to when data should be collectedcollected

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Recent arch historyRecent arch history

– For past two decades an architect’s point of For past two decades an architect’s point of highest leverage has been microarchitecturehighest leverage has been microarchitecture

Re-use what worksRe-use what works

– Pipelining, caches, shared buses, superscalar

Invent where necessaryInvent where necessary

– Microdataflow/OOO, trace caches, speculative branch predictors, cache coherency

With some major ISA work on RISCsWith some major ISA work on RISCs

– But this is changing. But this is changing. Right now.Right now.

CPU architects must evolve into system designersCPU architects must evolve into system designers

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System Designers todo listSystem Designers todo list

““Whatever needs doing” has become…Whatever needs doing” has become…1.1. Products, not CPUsProducts, not CPUs

2.2. Power-constrained system design Power-constrained system design

3.3. Multicore (gotta pay the bills, too)Multicore (gotta pay the bills, too)

4.4. Reliable systems from unreliable Reliable systems from unreliable componentscomponents

No longer “what I’d like to sell you” but No longer “what I’d like to sell you” but designing what buyers wantdesigning what buyers want

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Products Not CPUsProducts Not CPUs

“PC era” Ubiq. comp.

2004

Time

$$$

iPOD“killer apps” + PC’s

Cell phonesRay tracing

Portable computing

“Speed at any price” “What’s in it for me?” -buyer

“killer products”

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Power-constrained designPower-constrained design

““fast as possible at max power” will yield to fast as possible at max power” will yield to “fast enough, no faster”“fast enough, no faster”

– Lesson from the embedded spaceLesson from the embedded space

Thermal variability vs. guaranteed real-timeThermal variability vs. guaranteed real-time– Throw in wireless links for good measureThrow in wireless links for good measure

Battery life, not just cooling costBattery life, not just cooling costGlobal warming, energy crisis loomsGlobal warming, energy crisis looms

– It ain’t just cars and oil pricesIt ain’t just cars and oil prices

– Be synchronized to public taste or loseBe synchronized to public taste or lose

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MulticoreMulticore

““Here I come, ready or not…”Here I come, ready or not…”We can build ‘em. Can we…We can build ‘em. Can we…

– Compile to them?Compile to them?

– Feed them? (bandwidth)Feed them? (bandwidth)

– Cool them? (power)Cool them? (power)

– Write apps for them?Write apps for them?

Clear and present challengeClear and present challenge– There are pots of gold associated w/ thisThere are pots of gold associated w/ this

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Reliable Systems from Reliable Systems from Unreliable ComponentsUnreliable ComponentsN-mod redundancy too expensiveN-mod redundancy too expensiveTransient errors, manufacturing Transient errors, manufacturing

defects, design errorsdefects, design errors– Must survive them allMust survive them all

– Solution can’t drive power upSolution can’t drive power up

– Still want guaranteed performance for real-timeStill want guaranteed performance for real-time

Intel’s Shekhar Borkar says we have at Intel’s Shekhar Borkar says we have at most 10 years to figure this outmost 10 years to figure this out

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AdjurationsAdjurations

Computer revolution is only getting Computer revolution is only getting startedstarted

Role of architects is changingRole of architects is changing– If we don’t do it who will?If we don’t do it who will?

Your grandchildren will thank youYour grandchildren will thank you– And wonder if they’re as smart as you were And wonder if they’re as smart as you were

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backupsbackups