1. 1 Multicores viewed from a correctness perspective Ganesh Gopalakrishnan

2. 2 Can’t bury head in sand (adapted from Paul Petersen’s slide) l “Parallelism for Everyone” l Parallelism changes the game – A large percentage of people who provide applications are going to have to care about parallelism in order to match the capabilities of their competitors. Performance GHz Era Time Multi-core Era Active ISV Passive ISV Platform Potential Growing gap! Fixed gap

3. 3 The Need for Unified Solutions “There isn’t such a thing as Republican clean air or Democratic clean air. We all breathe the same air.” There isn’t such a thing as an architectural- only solution, or a compilers-only solution, or a programming methodology-only solution to the multicore menace

4. 4 Post-silicon correctness Specification Validation Design Verification Testing for Fabrication Faults Post-Silicon Verification product Does functionality match designed behavior? Pre-manufacture Post-manufacture

5. 5 Memory Consistency Models l Architectural, Language, Library mem models P1P2Pn Memory Cell 1 Memory Cell 2 Memory Cell n … Pi

6. 6 One Size Doesn’t Fit All (Adapted from “The Problem with Threads [Ed Lee]” l Direct use of weak shared memory – Lock-free queues used in latest MPICH2 – Bugs can silently corrupt numerical simulation data [ Gropp ] l Locks – Still fine within carefully defined units l Transactions – Look, Ma, No Locks !! l Message Abstractions – MPI meets multicore - challenges l Synchronous Parallel Notations – If we can express concurrency in deterministic ways, debugging and compositional reasoning are going to be facilitated

7. 7 Now you see it; Now you don’t ! On the menace of non reproducible bugs. l Deterministic replay must ideally be an option l User programmable schedulers greatly emphasized by expert developers l Runtime verification methods are being emphasized by our group now – Solutions in the works for MPI and PThreads

8. 8 It’s not just the memory wall, baby! It’s mainly the intellectual complexity wall Significant advances in formal semantics and verification methods must occur, with a huge emphasis placed on handling concurrency

9. 9 Are you an optimist?… (courtesy of Al Geist)