The Gathering Storm:

OSs and VMMs meet Many-Core

Mike SwiftUniversity of Wisconsin-

Madison

What will change?» Lots of execution contexts

» Some extra, but not many

» High application demand for parallelism

» Low-overhead communication and synchronization

» Heterogeneous processors» Statically and dynamically

» Closely-coupled systems» Shared caches, buses

Challenges

» Single thread performance has flattened» OS overhead matters more» Must reduce single-thread overhead

» Must perform more work asynchronously

Opportunities

» Hardware support for synchronization and fast communication» Fine-grained parallelism within the kernel

» Transactional memory to simplify kernel coding

Opportunities

» Extra hardware threads for background tasks» Monitoring» Optimization» Redundant execution

Challenges

» Scheduling matters again» We have to read all those gang scheduling papers

» OS must to manage diverse resources

» Set of resources may change» Threads may interfere» Application demand may change

Challenges

» Dynamic hardware» OS or VMMs must tolerate CPU addition, removal, change in properties

Challenges

» Scalability» Existing SMP, ccNUMA techniques difficult to apply, reduce single-thread performance

» Partitioning approaches limit resources to applications

Opportunities

» Possible new OS structures for scalability» Adopt supercomputer approach with OS nodes, compute nodes

» Multiple quasi-independent kernels

» Independent kernels with DSM for large applications

Are we up to it?

Challenges

» Interference» OS must account for interference between threads

» Hardware must provide measurements of interference