Todd Austin University 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-drawn circuits Basic logic synthesis Static circuit optimization Hardware Construction Typical-case optimization

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 Error comparator RAZOR FF clk_del Main Flip-Flop clk Shadow Latch Q1 D1 0 1 re co ve r IF Razor FF ID Razor FF EX Razor FF MEM (read-only) WB (reg/mem) error b u b bl e recover Razor FFStabilizer FFPC recover flus hID b u b bl e error b u b bl e flus hID error b u b bl e flus hID Flush Control flus hID error

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) CM Proc CM Proc CM Proc Keystore Req Scheduler In QOut Q requests results Pipelined 32-Bit MUL 1K Byte SBOX Cache 32-Bit Adder 32-Bit Rotator XORAND Logical Unit XORAND Logical Unit {tiny} {short} {tiny} {long}

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-drawn circuits Basic logic synthesis Static circuit optimization Hardware Construction Typical-case optimization Composable H/W acceleration