Todd AustinUniversity of Michigan

X-Stack Energy Optimization:Fact or Fiction

2

Austin’s Theory of Inevitable H/W Progression

Hand coding

Basic compilation

Static optimization

Profile-guided optimization

Run-time code generation and optimization

Software Construction

Hand-drawncircuits

Basic logicsynthesis

Static circuitoptimization

Hardware Construction

Typical-caseoptimization

X-Stack

Razor Typical-Case Optimization

Circuit-level Razor latch detects timing errors

Architecture-level pipeline recovery sequence fixes pipeline state after timing error

Operating system-level voltage control sets energy level to minimize error rates

50% energy savings for < 1% performance loss

Error_L

Errorcomparator

RAZOR FF

clk_del

Main Flip-Flop

clk

Shadow Latch

Q1D101

recover

IF

Razo

r FF

ID

Razo

r FF

EX

Razo

r FF

MEM(read-only)

WB(reg/mem)

errorbubble

recover recover

Razo

r FF

Stab

ilize

r FF

PC

recover

flushID

bubble

errorbubble

flushID

errorbubble

flushID

FlushControl

flushID

error

X-Stack

CryptoManiac Typical-Case Optimization

Circuit-level functional unit design tucks pre- and post-Boolean ops into clock cycle

Architecture-level ISA extension exposes pre/post-ops

Application-level programming re-expresses algorithms to leverage optimization

20% performance benefit (could recast as energy benefit)

CMProc

CMProc

CMProc

Keystore

Req

S

ched

ule

r

In Q Out Q

requests

.

.

.

results

Pipelined32-BitMUL 1K Byte

SBOXCache

32-BitAdder

32-BitRotator

XOR ANDLogical Unit

XOR ANDLogical Unit

{tiny}

{short}

{tiny}

{long}

X-Stack

X-Stack Optimization Thoughts

Opportunities– Big design wins to be found for x-stack optimizations

Challenges– Approach destroys abstractions, places burdens on layers up

the stack (e.g., architects and programmers)– Typically need to work outside of your comfort zone– Reviewers are often skeptical of x-stack modeling fidelity

Advice– Play well with others (seek effective collaborations)– Be open to learning new technologies/applications/fields– Be prepared to pursue physical demonstrations

6

Austin’s Theory of Inevitable H/W Progression

Hand coding

Basic compilation

Static optimization

Profile-guided optimization

Run-time code generation and optimization

Software Construction

Hand-drawncircuits

Basic logicsynthesis

Static circuitoptimization

Hardware Construction

Typical-caseoptimization

ComposableH/W acceleration

X-StackX-Stack