Charisma: Orchestrating Migratable Parallel Objects

Charisma: Orchestrating Migratable Parallel Objects Chao Huang, Laxmikant Kale Parallel Programming Lab University of Illinois at Urbana-Champaign

Motivation • Complex structures in modern applications • Large number of components • Complicated interactions • Parallel programming productivity • Traditional SPMD paradigms break modularity • Object-based paradigm obscures global control flow • Goal • A language for expressing global view of control HPDC 2007

Outline • Motivation • Expressing Flow of Control • Language Design and Implementation • Code Examples • Results • Performance and Productivity Studies • Related Work • Future Work HPDC 2007

Example: MD MPI_Recv(angle_buf,…, ANGLE_SRC, ANGLE_TAG,…); /* calculate angle forces */ MPI_Recv(pair_left_buf,…, PAIR_LEFT_SRC, PAIR_LEFT_TAG,…); MPI_Recv(pair_right_buf,…, PAIR_RIGHT_SRC, PAIR_RIGHT_TAG,…); /* calculate pairwise forces */ • Structure of a simple MD simulation MPI_Recv(buf,..., MPI_ANY_SOURCE, MPI_ANY_TAG,…); switch(GET_TYPE(buf)){ case (FOR_ANGLE): /* calculate angle forces */ case (FOR_PAIR_LEFT): /* calculate pairwise forces */ case (FOR_PAIR_RIGHT): /* calculate pairwise forces */ } patch (cell) compute (cellpair) HPDC 2007

Expressing Flow of Control • Charm++: fragmented in object code MainChare::MainChare{ cell.sendCoords();}MainChare::reduceEnergy(energy){ totalEnerty+= energy; if iter++ ( MAX_ITER cells.sendCoords(); else CkExit();} Cellpair::recvCoords(coords){ if not coords from both cells received buffer(coords); return; else // all coords ready force = calcForces(); for index in 2 cells cells(index).recvForces(forces);} Cell::sendCoords(){ for index in 26 neighbor cellpairs cellpairs(index).recvCoords(coords);}Cell::recvForces(forces){ totalforces += forces; if not all forces from all cellpairs received return; else // neighborhood reduction completed integrate(); mainProxy.reduceEnergy(energy);} HPDC 2007

Charisma • Expressing global view of control • Parallel constructs in orchestration code • Sequential code separately in user C++ code • Features • High level abstraction of control • Separation of parallel constructs and sequential code • Generating Charm++ code • Automatic load balancing, adaptive overlap, etc HPDC 2007

Language Design • foreach statement • Invokes method on all elements: object-level parallelism • Producer-consumer model • Sequential code unaware of source of input values and destination of output values • Data is sent out as soon as it becomes available • Various communication patterns • Control constructs: loop, if-then-else, overlap foreach i in workers workers[i].doWork(); end-foreach foreach i in workers (p[i]) <- workers[i].foo(); workers[i].bar(p[i+1]); end-foreach HPDC 2007

Code Example: MD with Charisma • Orchestration code: global view of controlforeach i,j,k in cells (coords[i,j,k]) <- cells[i,j,k].produceCoords(); end-foreach for iter = 1 to MAX_ITER foreach i1,j1,k1,i2,j2,k2 in cellpairs (+forces[i1,j1,k1],+forces[i2,j2,k2]) <- cellpairs[i1,j1,k1,i2,j2,k2]. calcForces(coords[i1,j1,k1],coords[i2,j2,k2]); end-foreach foreach i,j,k in cells (coords[i,j,k],+energy) <- cells[i,j,k].integrate(forces[i,j,k]); end-foreach MDMain.updateEnergy(energy); end-for HPDC 2007

Code Example: MD with Charisma • Sequential code void Cell::integrate(Force forces[], outport coords, outport energy){ for(int i=0;i<mySize;i++){ myAtoms[i].applyForces(forces[i]); myAtoms[i].update(); } produce(coords,myAtoms,mySize); double myEnergy = this->calculateEnergy(); reduce(energy, myEnergy, “+”); } HPDC 2007

Language Implementation • Dependence analysis • Identify inports and outports • Organize dependence graph • Generate communications • Control transfer • Central control vs. Distributed control • Generated code optimization • Eliminating unnecessary memory copy • Migrating live variables • Library module support HPDC 2007

Expressing Flow of Control (Cont.) • Example: Parallel 3D FFT • foreach x in planes1 • (pencils[x,*]) <- planes1[x].fft1d(); • end-foreach • foreach y in planes2 • planes2[y].fft2d(pencils[*,y]); • end-foreach HPDC 2007

Results • Scalability Results 2D Jacobi (Size: 163842 on 4096 objects) 3D FFT (Size: 5123 on 256 objects) HPDC 2007

Results • Productivity Study 2D Jacobi Wator HPDC 2007

Related Work • Producer-consumer model • Fortran M • Composing from components • P-COM2 • Visual parallel dataflow languages • HeNCE and CODE • VPE HPDC 2007

Future Work • Use dependence to optimize • Critical path analysis • Prefetch objects (out-of-core execution) • Assist communication optimizations • Orchestration for other fields • Stream-based applications HPDC 2007

Thank You • Questions? • More details at http://charm.cs.uiuc.edu HPDC 2007

Charisma: Orchestrating Migratable Parallel Objects