Compiling Application-Specific Hardware

Mihai Budiu

Seth Copen Goldstein

Carnegie Mellon University

Resources

Problems

• Complexity

• Power

• Global Signals

• Limited issue window => limited ILP

We propose a scalable architecture

Outline

• Introduction• ASH: Application Specific Hardware

• Compiling for ASH• Conclusions

Application-Specific HardwareC program

Compiler

Dataflow IR

Reconfigurable hardware

Our Solution

General: applicable to today’s software - programming languages

- applications

Automatic: compiler-driven

Scalable: - run-time: with clock, hardware - compile-time: with program size

Parallelism: exploit application parallelism

Asynchronous Computation

+

data

datavalid

ack

New

• Entire C applications

• Dynamically scheduled circuits

• Custom dataflow machines

- application-specific

- direct execution (no interpretation)

- spatial computation

Outline

• Scalability• Application Specific Hardware• CASH: Compiling in ASH

• Conclusions

CASH: Compiling for ASH

Memory partitioning

Interconnection net

Circuits

C Program

RH

Primitives+Arithmetic/logic

Multiplexors

Merge

Eta (gateway)

Memory

data

predicates

datapredicate

ld st

Forward Branches

if (x > 0) y = -x;

elsey = b*x;

*

xb 0

y

!

- >

Decoded mux

Conditionals => Speculation

Critical Paths

if (x > 0) y = -x;

elsey = b*x;

*

xb 0

y

!

- >

Lenient Operations

if (x > 0) y = -x;

elsey = b*x;

*

xb 0

y

!

- >

Solve the problem of unbalanced paths

!

ret

i

+1< 100

0

*

+

sum

0

Loops

int sum=0, i;

for (i=0; i < 100; i++)

sum += i*i;

return sum;

Control flow => data flow

Compilation

• Translate C to dataflow machines

• Optimizationssoftware-, hardware-, dataflow-specific

• Expose parallelism – predication– speculation– localized synchronization– pipelining

Pipeliningi

+

<=

100

1

*

+

sum

pipelinedmultiplier

Pipeliningi

+

<=

100

1

*

+

sum

Pipeliningi

+

<=

100

1

*

+

sum

Pipeliningi

+

<=

100

1

*

+

sum

Pipeliningi

+

<=

100

1

*

+

sum

i’s loop

sum’s loop

Longlatency pipe

Pipeliningi

+

<=

100

1

*

+

sum

Pipeliningi

+

<=

100

1

*

+

sum

i’s loop

sum’s loop

Longlatency pipe

predicate

Predicate ackedge is on thecritical path.

Pipeliningi

+

<=

100

1

*

+

sum

critical pathi’s loop

sum’s loop

Pipeliningi

+

<=

100

1

*

+

sum

i’s loop

sum’s loop

decouplingFIFO

Pipeliningi

+

<=

100

1

*

+

sum

i’s loop

sum’s loop

critical path

decouplingFIFO

ASH Features

• What you code is what you get– no hidden control logic– lean hardware

(no CAM, multi-ported files, etc.)– no global signals

• Compiler has complete control

• Dynamic scheduling => latency tolerant

• Natural ILP and loop pipelining

Conclusions

• ASH: compiler-synthesized hardware from HLL

• Exposes program parallelism

• Dataflow techniques applied to hardware

• ASH promises to scale with:

– circuit speed

– transistors

– program size

Backup slides

• Hyperblocks• Predication• Speculation• Memory access• Procedure calls• Recursive calls• Resources• Performance

Hyperblocks

Procedure back

Predication

p !p

q

if (p) .......q

if (!p) .......

hyperblock

back

Speculation

q

if (!p) ......

q

if (!p) ......

ops w/ side-effects

back

Memory Access

back

load

addresspredicate

token

tokendataLoad-store

queue

store

address pred token

token

data

Inte

rcon

nect

ion

netw

ork

Memory

Procedure calls

back

Inte

rcon

nect

ion

netw

ork

Extract args

ret

result caller

Procedure P

call P

args

Recursion

recursive call

save live values

restore live values

hyperblock

stack

back

Resources

• Estimated SpecINT95 and Mediabench

• Average < 100 bit-operations/line of code

• Routing resources harder to estimate

• Detailed data in paper

back

Performance• Preliminary comparison with 4-wide OOO• Assumed same FU latencies• Speed-up on kernels from Mediabench

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