General Purpose Processors as Processor Arrays

Peter Cappello

UC, Santa Barbara

VLSI Design Forces in 1986

“Nature, to be commanded, must be obeyed.” – Sir Francis Bacon

• High performance parallelism

VLSI Design Forces in 1986

• High performance parallelism

VLSI Design Forces in 1986

• Power is scarce limit resistive delay

VLSI Design Forces in 1986

• Power is scarce limit resistive delay

limit long communication

VLSI Design Forces in 1986

• Power is scarce limit resistive delay

limit long communication

• Area is scarce limit wire crossing

VLSI Design Forces in 1986

• Power is scarce limit resistive delay

limit long communication

• Area is scarce limit wire crossing

VLSI Design Forces in 1986

• Power is scarce limit resistive delay

limit long communication

• Area is scarce limit wire crossing

VLSI Design Forces in 1986

• $$ are scarce design is expensive

VLSI Design Forces in 1986

• $$ are scarce design is expensive

reuse components

VLSI Design Forces in 1986

• $$ are scarce design is expensive

reuse components

VLSI Design Forces in 1986

• $$ are scarce design is expensive

reuse components

VLSI Design Forces in 1986

• $$ are scarce design is expensive

reuse components

VLSI Design Forces in 1986

• $$ are scarce design is expensive

reuse components

VLSI Design Forces in 1986

In 2D systolic arrays, clock skew is an issue wavefront arrays

Islands of synchrony inan ocean of asynchrony

Processor Array Properties

1. Have multiple processors

Processor Array Properties

1. Have multiple processors

2. Neighbors abut (no long wires)

Processor Array Properties

1. Have multiple processors

2. Neighbors abut

3. Only neighbors communicate directly

Processor Array Properties

1. Have multiple processors

2. Neighbors abut

3. Only neighbors communicate directly

4. Have a constant # of processor types

Processor Array Properties

1. Have multiple processors

2. Neighbors abut

3. Only neighbors communicate directly

4. Have a constant # of processor types

5. Scale: larger problems larger arrays

No 3D PA Has Properties 1 - 5

Enclose 3D PA in minimal sphere of radius r.

r

No 3D PA Has Properties 1 - 5

Scale PA in all 3 dimensions.

r

No 3D PA Has Properties 1 - 5

1. Power consumption = Θ( r3 ).

r

No 3D PA Has Properties 1 - 5

1. Power consumption = Θ( r3 ).

2. Heat dissipation via surface = Θ( r2 ).

r

VLSI Design Forces in 2006

“Nature, to be commanded, must be obeyed.”

– Sir Francis Bacon

• Power is scarce limit clock frequency

parallelism

• Power is scarce limit resistive delay

limit long communication

Trends in GPP in 2006

• Chip multiprocessors (CMP)

• Vector IRAM

• Cell

• TRIPS

• RAW

Trends in GPP in 2006

Chip Multiprocessors (CMP)– Parallel processors– Crossbar

Trends in GPP in 2006

Vector IRAM – Vector Intelligent RAM

• For mobile multimedia devicesStream data processing

• Combine GPP and DSP– Parallel – linear array– Crossbar

Trends in GPP in 2006

Cell processor“The Department of Energy said Wednesday that it had

awarded I.B.M. a contract to build a supercomputer capable of 1,000 trillion calculations a second, using an array of 16,000 Cell processor chips that I.B.M. designed for the coming PlayStation 3 video game machine.” Sept. 7, 2006. NY Times.

• Parallel processors – BIU – Bus interface unit– RMT – Replacement management table– SL1 – 1st-level cache– PPE – PowerPC Element– SPE – Synergistic Processor Element– Element interconnect bus

Trends in GPP in 2006

• TRIPSTera-op, Reliable, Intelligently adaptive

Processing System

The following slides are taken from a talk:

"The Design and Implementation of the TRIPS Prototype Chip," HotChips 17, Palo Alto, CA, August, 2005.

• E – execution tile

• R – register bank

• D – 8KB data cache

• I – instruction cache

• G – global control

• Instructions execute as a data flow graph– An instruction’s output

is another instruction’s input.

– Minimize use of register/cache for intermediate values

• Register reads/writes access the register banks

• Loads/stores access the data cache banks

Trends in GPP in 2006

RAW (MIT)The following slides are taken from a RAW talk:

Evaluating The Raw Microprocessor: Scalability and Versatility Presented at the International Symposium on Computer Architecture, June 21, 2004.

ALU

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RF>>

+

Replace the crossbar with a point-to-point, pipelined, routed network.

Distribute the Register File

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RF

RFRF RFRF

RFRF RFRF

RFRF RFRF

RFRF RFRF

Distribute the rest.

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RFRF RFRF

RFRF RFRF

RFRF RFRF

RFRF RFRF

Control

WideFetch

(16 inst)

UnifiedLoad/Store

Queue

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[ISCA99]

Tiles!

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RFRF RFRF

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Conclusions•VLSI Scalable microprocessors are possible.

Constant factors are beginning to give way to asymptotics: - 16 ALU Raw – Oct 2002 - 64 ALU Raw – Now - 1,024 ALU Raw - 2010 - 32,768 ALU Raw – If Moore’s Law makes it to 2 nm•There is an opportunity to make processors more

“versatile” i.e., steal applications from custom chips.

•Tiled Processor Architectures are a promising approach and merit further research.

GPP Predictions: In 10 Years

• Encapsulate registers/cache/processors into an array.

• Partition off-chip memory: Encapsulate memory & processor.

Safely increase parallel access (concurrent programming)

• For non-recursive applications GPP (mobile multimedia):

– no bus; quasi-nearest neighbor networks.

• For recursive applications GPP (gaming, control)

– replace bus w/ lean on-chip short-diameter communication network.

– 1 network-on-chip routes register/cache/instruction/control.

– Need >= 1K processors/chip to justify network-on-chip.

Predictions

• Increasing complexity of:– Applications– Technology

Increasing specialization of labor

Predictions

• Increasing complexity of:– Applications– Technology

Increasing specialization of labor

• Rate of change of increase in complexity is increasing over time Increasing adaptability is important!

Yet another taxonomy!

RECONFIGURABILITY

ARCHITECTURALSPECIFICITY

ASICPROTOTYPEASIC

GPP CCM

STATIC DYNAMIC

SPECIFIC

GENERAL

Yet another taxonomy!

ASICPROTOTYPEASIC

GPP CCM

STATIC DYNAMIC

SPECIFIC

GENERAL

ARCHITECTURALSPECIFICITY

RECONFIGURABILITY

STATIC DYNAMIC

COMMUNICATIONLATENCY

TP

DP

ASICPROTOTYPEASIC

GPP CCM

ARCHITECTURALSPECIFICITY

SPECIFIC

GENERAL

RECONFIGURABILITY

DP Communication Topology

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

EDGE ISA(2D VLIW)

With CoresFFT, RISC

High Throughput (iterative)Communication topology

TP Communication Topology

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

FPGA FPGA

EDGE ISA(2D VLIW)

With CoresRAM, RISC

Low Latency (recursive)Communication topology

General PurposeLanguage

Domain SpecificLanguage

Computational Model

ComputeSubstrate

CommunicateSubstrate

ConfigurableHardware

StaticHardware

Fabrication Technology

DISCIPLINE PROCESS

CS, DE

CS, CE

CE, EE

EE

EE, ME

Circuit layout

Processor architecting

CompilingCS

CS, DE

Application programDE

CE, EE Processor layout

FPGA/Circuit design

Language design

Fabrication process

Compute model design

Conclusion

• Last 20 years witnessed dramatic advances

Conclusion

• Last 20 years witnessed dramatic advances

• Next 20 years will witness even more dramatic advances.

Spare slides follow

Recursive Computation via a Tree of Meshes Network?

Quasi-Scalable

Quasi-Scalable

Quasi-Scalable

RF D$ GLOBAL LOCAL

ADDRESS

Interleave Memory & Processor Tiles

• Slightly more chips

• Compiler localizes memory

accesses

• EDGE ISA deals with

variable access times

(TRIPS).

Cell architecture

Specialization of LaborHigh Level / Domain-Specific

Language

Computational ModelExposes Comm. Topology

ISA Network

FPGA

Fabrication

APPLICATIONPROGRAMMER

COMPILER

COMPUTERARCHITECT

COMPUTERENGINEER

ELECTRICAL &COMPUTERENGINEER