Josh Fisher
Bob Rau Award Talk
Except for a very short talk at Mateo
2012, I haven’t given a talk in six years.
I haven’t even kept up with the field.
A talk on The Lefty’s Advantage in Tennis
(I could do that well!) wouldn’t work.
So what to do...
AWARD: For the development of trace scheduling
compilation and pioneering work in VLIW (Very
Long Instruction Word) architectures.
• I’m very proud of having done all that, and am truly
honored to be receiving this award.
• And so it is with great trepidation—
—that
I say I did something else I’m equally proud of.
• I bring it up because I want to give advice: I think it
hurts our science that it isn’t the kind of thing people
get awards for. I wish that when (other) people do this
sort of thing, they would get recognized.
From John Hennessey’s Keynote/Review
(1998) of The First 25 Years of ISCA.
In the 1960-1970s, there were three different
communities doing ILP
Dynamic ILP:
1. The general-purpose supercomputers of the day, and
the scalar units of the vector machines that followed.
Static ILP:
2. Horizontal microcode (here at Micro, “The
Microprogramming Workshop”!).
3. Array processors/bit slice processors (e.g. for custom
graphics).
None acted like the others existed.
It was real ILP: CDC 6600 / IBM Stretch
“The paper did present an ingenious method of rearranging the
linear structure of a calculation and of departing from a linear
structure and carrying out operations in parallel. ” Discussion
involving Alan Perlis, John Backus, Robert Floyd, Maurice Wilkes,
and others [1964].
“If this approach is carried further in the coming years, processors
may contain tens or hundreds of independent arithmetic units. …
Ultimately, the problem of efficiency will fall on the compilers and
the compiler writers.” [Stone, 1967].
“... stores must be inhibited while fetches are in progress, and vice
versa. This feature makes it infeasible to extend this design to
include parallelism on a very large scale. ” [Schwartz, 1966].
(The later “MAXPAR” experiments made the pessimism worse.)
At Micro, We Worried About
“Horizontal Microcode Compaction”
• It was one of the most popular research topics here.
• We were trying to automatically turn vertical (sequential)
microcode into horizontal (instruction-level parallel) microcode.
There was some awareness of horizontal microcode in the Array
Processor/Bit Slice crowd (Bob Rau in particular bridged that gap in
the 1980s).
I was lucky enough to be in the right place
(Courant) at the right time (the 1970s) to see
and name this commonality among subjects.
There is Real Value In This Commonality!
Something Similar: The “Invention” of RISC,
and the RISC vs. CISC Wars.
The real topic was “instruction complexity”.
• Of course there were
IBM/Berkeley/Stanford!
“ RISC ”
architectures
before
• The subject that was invented was the debate about instruction
complexity.
• Although people often talked about instruction complexity before,
it became a subject, a concept, with Cocke/Patterson/Hennessey
promoting RISC. They framed a debate.
Something Similar: The “Invention” of RISC,
and the RISC vs. CISC Wars.
The real topic was “instruction complexity”.
• Work like Clark/Emer shed real light on the subject—it was much
easier to see its value once the area was in sharp relief. Much
more research like that should have been promoted.
• We weren ’ t stuck with dumb market-based arguments only.
“Such and such is better because it won in the marketplace.”
Though there is always a lot of that.
(Doing better than that is our job as researchers.)
a few words about…
Multiflow Computer
1984-1990
Multiflow’s Architectural Claim to Fame
Multiflow is well-known for having demonstrated the
practicality of VLIW architectures and their compilers.
In the early 1980s, nearly everyone was very skeptical
about this.
e.g. Bob Colwell:
Then Josh walked into my office, on a visit to CMU. After an
hour of earnest discourse, he had moved me from default
skeptic to “if there’s something insurmountable here, it’s
not obvious what it is. And he seems very reasonable,
given that he’s nuts.”
Multiflow’s Architectural Claim to Fame
e.g. Ray Simar, TI, in 1997: “I remember looking at the idea
and saying these guys were nuts, ... I thought there was no
way it would work in the real world.”
But … “At the end of the day what we thought was ridiculous
was the best solution,”
VLIW in relationship to marketplace forces has
been, and continues to be, a tumultuous ride,
but no one ever again called it impractical. (Or
me nuts. Well, maybe some people.)
Multiflow’s Architectural Claim to Fame
But there is a second thing the Multiflow should also be known for:
When you consider code development as well as use:
I claim that the Trace was the most exotic/novel/different
processor ever to be used as an ordinary computer.
You compiled and ran, and got good performance.
Even though the computer might have 1,024-bit instructions.
Over time, many bizarre architectures have been proposed, but
none have been programmed and used as ordinary computers.
It was true in 1987, and 25 years later, it’s still true.
The way the market has gone, it may always be true.
Multiflow Also Produced Four Fellows at
Major Computer Companies
• Dave Papworth
• Bob Colwell
• Geoff Lowney
• Josh Fisher
Notable Minisupercomputer Companies
(Wikipedia)
• Ametek
• IBM (ES/9121 w/ Vector Facility)
• Alliant Computer Systems
• ICL (DAP)
• American Supercomputer (Mike Flynn)
• Kendall Square Research
• Astronautics (Jim Smith)
• Key Laboratories
• BBN
• MasPar
• Convex Computer
• Meiko Scientific
• Culler Harris
• Multiflow Computer (Josh Fisher)
• Culler Scientific
• Myrias
• Cydrome (Bob Rau)
• Prisma
• DEC (VAX 9000)
• Parsytec
• Elxsi
• Pyramid Technology
• Encore Computer
• Scientific Computer Systems
• Evans & Sutherland
• Sequent
• Flexible Computer
• Solbourne
• Floating Point Systems
• SUPRENUM
• Guiltech/SAXPY (Rob Schreiber)
• Supertek Computers
• HAL Computer Systems
• Thinking Machines Corporation
The Preface and
Table of Contents
are available at:
MultiflowTheBook.com
I know I’m hardly an
unbiased reviewer,…
…but I really recommend
this book to people
interested in a startup
that sprang from this
community.
It is an amazing story.
Info@MultiflowTheBook.com
http://MultiflowTheBook.com
Table of Contents
Preface
Product Introduction
The Eureka Moment
No Vectors
Yale
Le Flic
VLIW
Selling the Trace
John and John
Doldrums
Three Guys and a Car
Europe
Multiflow Computer
The End
Don Eckdahl
Epilogue
The Engineering Team
Josh’s Technical Appendix
Building the Trace
Sources and Further Reading
Lx is very much inspired by the Multiflow Trace
Lx resulted in STMicroelectronics’ ST200 Family
Here are two Lx
cores on an
STMicroelectronics
SOC.
ST uses Lx in
digital video SOCs.
Guess how many
Lx cores STM has
sold??
(And HP has put a good many more in their printers.)
A fanatic is someone
who can’t change his
mind, and won’t change
the subject.
Attributed to Winston Churchill
Multiflow was in business 1984 - 1990
Multiflow’s computers cost between about $350k-$750k.
How many systems do you think were sold??