What Computer Architects

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8 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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What Computer Architects
Really Do

Bob Colwell

E
-
M Talk ISCA ‘05

“Or should.”

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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

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Is there a trend here…

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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
.”

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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

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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
.

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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

CPU

system

CPU
-
Mesmerization. Root cause? Profits.

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IA32+64
-
bit exts

IA32

CPU architect

64
-
bit extensions to IA32

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Multicore

$100B industry

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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…

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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

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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.


CPU architects must evolve into system designers


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System Designers todo list

“Whatever needs doing” has become…

1.
Products, not CPUs

2.
Power
-
constrained system design

3.
Multicore (gotta pay the bills, too)

4.
Reliable systems from unreliable
components


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

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Products Not CPUs

“PC era”

Ubiq. comp.

2004

Time

$$$

iPOD

Cell phones

Ray tracing

Portable computing


“Speed at any price”

“What’s in it for me?”
-
buyer

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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

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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

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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

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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


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backups