automatically exploiting cross-invocation parallelism using runtime ...

for (int i = 0; i < framenum; i++) {L1: ClearParticles();L2: RebuildGrid();L3: InitDensitiesAndForces();L4: ComputeDensities();L5: ComputeDensities2();L6: ComputeForces();L7: ProcessCollisions();L8: AdvanceParticles();}Figure 5.5: Outermost loop in FLUIDANIMATEported in the Liberty parallelizing compiler infrastructure due to frequent manifesting crossiterationdependences and irregular memory access patterns. The outermost loop is composedof eight consecutive inner loops.Inner loop L4 and L6 can be parallelized byDOANY, LOCALWRITE or DOMORE, while all the other inner loops can be parallelizedby DOALL. As a result, a variety of parallelization plans can be applied.The manually parallelized version of FLUIDANMIATE in Parsec benchmark suite dividesthe shared data grids among threads. It applies DOANY to inner loop L4 and L6and DOALL to the other inner loops. Pthread barriers are inserted between two inner loopinvocations to respect cross-invocation dependences. To protect the shared data structure,DOANY applies locks to guarantee atomic accesses. Meanwhile, to avoid over synchronizationcaused by locks, it allocates an array of locks instead of using a single globallock. Each lock protects a section of the shared data structure. Threads accessing differentsections of the shared data do not have to synchronize at the same lock. Figure 5.6 demonstratesthe performance improvement of the manual parallelization. Since the manual parallelizationonly supports thread number that is to the power of 2, only three performanceresults are shown in the figure.Other than DOANY, inner loops L4 and l6 can also be parallelized by LOCALWRITE89