SMALL IDENTIFIERS FOR CHARE ARRAY ELEMENTS Phil Miller With contributions from Akhil Langer, Harshitha Menon, Bilge Acun, Ramprasad Venkataraman, and L.V.
Download ReportTranscript SMALL IDENTIFIERS FOR CHARE ARRAY ELEMENTS Phil Miller With contributions from Akhil Langer, Harshitha Menon, Bilge Acun, Ramprasad Venkataraman, and L.V.
SMALL IDENTIFIERS FOR CHARE ARRAY ELEMENTS Phil Miller With contributions from Akhil Langer, Harshitha Menon, Bilge Acun, Ramprasad Venkataraman, and L.V. Kalé Array Element Location Management Enables process virtualization Directs messages from sender PE to host PE Maps element identifier to object pointer on host PE Processes element instantiation & deletion Placement at creation On-demand creation Detects duplicate insertion Array Element Location Management Hooks for RTS introspection and adaptivity Tracing Load instrumentation Migration Fault tolerance Array Index Structure Fixed 16 bytes No less, even for small/simple arrays No more, even for sophisticated arrays Home PE Track assigned elements Existence Current host PE Default host PE Tell other PEs as necessary Assigned by Array Map Static Array Maps Array Index to Home PE Simple strategies Block Round-robin (cyclic) File Application-specific OpenAtom CharmLU Pushing the Envelope Array message variant takes 34-38 bytes Next largest only needs 18 bytes Could save 16-20 bytes on every message! Goals of a shorter ID Reduce envelope size Shrink memory footprint Improve fine-grain performance Enable future index evolution Design parameters Preserve API: Send messages by index Maps and home PEs Avoid extra communication Maintain or improve performance Scheme 64 Bits Protocol Home PE generates ID at construction Simple counter in element field Async request if constructing elsewhere ID requests piggy-back on location requests Extra messages only for unusual construction Potential Optimizations PE-level caching & pointer lookups Index compression instead of lookups Index Compression Many arrays fit directly within 48-bit space All 1D with 32-bit ‘int’ 2D < (16M)2 Etc. Specify bounds, RTS will bit-pack if they fit Could also enable hashing Collisions would be disastrous Known indices and perfect hashing? Summary Current Status Implemented, passing all tests Performance Comparable in coarse-grain apps Slightly slower in fine-grain Future Direction: arbitrary index types AMR, tree codes