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Implementation: Charm++

Implementation: Charm++. Orion Sky Lawlor olawlor@acm.org. Background & Roadmap. Your code sits on Charm++ : Interface Translator .ci file, CProxy_*, parameter marshalling Arrays (Orion++) Reductions, broadcasts, migrations, pup Groups and Chares (``Milind++)

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Implementation: Charm++

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  1. Implementation:Charm++ Orion Sky Lawlor olawlor@acm.org

  2. Background & Roadmap • Your code sits on Charm++: • Interface Translator • .ci file, CProxy_*, parameter marshalling • Arrays (Orion++) • Reductions, broadcasts, migrations, pup • Groups and Chares (``Milind++) • Basic communication calls atop Converse • Basics (++) • Registration, readonlies, messages

  3. Where is it? • Charm++ core source code in charm/src/Common/ck-core/ • Gets soft-linked over and made in charm/net-linux/tmp/ • Headers in charm/net-linux/include/ • Code gets linked into the library charm/net-linux/lib/libck.a • This all gets used when you pass "-language charm++" to charmc

  4. Basics: • We need to be able to call some C++ method bar on user object foo • But the core`s never heard of foo • Solution: register a function pointer to a "call-method" function: void _call_foo_bar(void *msg,foo *obj) { obj->bar(msg); } ...at startup... int barEpIdx= CkRegisterEp(&_call_foo_bar,..);

  5. Registration & Startup • ck-core/register.h .C (300 lines) • At startup, each module registers its methods, which end up in a big entry method table • An entry point's index in this table is its int "epIdx", used everywhere • Translator writes this registration code (the call-method function, "__register" function) in .def file

  6. Groups & Chares (Milind++) • charm.h, ck.C (1000 lines) • Lowest layer of Charm++ • CkCreateChare, CkCreateGroup • CkSendMsg, CkSendMsgBranch • Quite simple, thin wrapper on Converse • Very stable-rarely changes • Callable from C (!)

  7. CkSendMsg(int epIdx, void *msg,CkChareID *to) • envelope *env = UsrToEnv(msg); • Finds Charm++ msg fields (see envelope.h) • env->setMsgtype(ForChareMsg); • env->setObjPtr(to->objPtr); • env->setEpIdx(epIdx); • env->setSrcPe(CkMyPe()); • CmiSetHandler(env, _charmHandlerIdx); • CldEnqueue(to->onPE, env, _infoIdx);

  8. CkSendMsg: Clutter • Various unrelated calls clutter up the Charm++ core (FIXME?) • Keep track of message sends; give "Message being re-sent..." diagnostic • _CHECK_USED(env); • _SET_USED(env, 1); • Trace message sends for projections • _TRACE_CREATION_1(env); • Notify quiescence detection of send • CpvAccess(_qd)->create();

  9. Arrays (Orion++) • Many interesting features: • Arbitrary indexed collection of Chares • Connects to load balancer • Supports migration, broadcasts, reductions • Not even clear some operations even possible • But much more complicated • Highly fragmented, er, factored code • Array Manager, Location Manager, Reduction Manager, Broadcaster, Reducer

  10. Arrays Diagram CkReductionMgr-- reductions CkLocMgr-- migration CkArray-- coordinator ArrayElement ArrayElement ArrayElement ArrayElement-- user's work

  11. CkReductionMgr • ckreduction.h .C .ci (1300 lines) • Accept contributions from local members of a migrating set of reduction "contributors" • Implemented as Group • Actually "IrrGroup", since normal groups inherit from CkReductionMgr. • Exactly one per array; but zero dependence on arrays • Arrays are just a client of CkReductionMgr

  12. Location-- CkLocMgr • ck-core/cklocation.h .C .ci (2000) • Keep track of location of migrating elements • Handles messaging and migration • Each array has a location manager • But a location manager may have several "bound" arrays, which will migrate together • Implemented as a group

  13. Array Manager-- CkArray • ck-core/ckarray.h .C .ci (1300 lines) • Keeps track of a set of local array elements • Implemented as a group • Glue that connects pieces of array system together: • Inherits from CkReductionMgr • Implements CkArrMgr (for location mgr) • Interfaces with proxies • Controls ArrayReducer, ArrayBroadcaster

  14. Pup • util/pup.h .C (1000 lines) • Used to migrate, parameter marshall • Heavy C++: overload the | operator • "Easy to use, tough to understand" • Bottom line: (user view) • Say "p|x;" for all your x's. • Bottom line: (system view) • We get a "void *" for each of the user`s x.

  15. Translator • xlat-i/xi-symbol.h .C (3000 lines) • Turn .ci files into .decl/.def files • Standalone program "charmxi" • Tokenize .ci with lexx: xi-scan.l • Parse .ci with yacc: xi-grammar.y • Turn parsed structures into .decl/.def • Almost completely routines named "gen*"-- code-generating routines • E.g., "Entry::genDecls"-- generate code in .decl file for an entry method

  16. Not Covered • Startup & Shutdown (init.C) • Quiescence detection (qd.C) • Dynamic load balancer (ck-ldb/) • Callbacks, futures (for sync methods), debug, TeMPO • Libraries (charm/src/Common/lib/) • TCharm, FEM, AMPI, MBlock, AMR, comm, ... • Details! Read manuals, headers, our minds...

  17. Conclusion • Interface Translator • .ci file, CProxy_*, parameter marshalling • Arrays (Orion++) • Reductions, broadcasts, migrations, pup • Groups and Chares (``Milind++) • Basic communication calls atop Converse • Basics (++) • Registration, readonlies, messages

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