Speculative Separation for Privatization and Reductions Nick P. Johnson Hanjun Kim Prakash Prabhu Ayal Zaksy David I. August Princeton University, Princeton, NJ yIntel Corporation, Haifa, Israel fnpjohnso, hanjunk, pprabhu,
[email protected] [email protected] Abstract Memory Layout Static Speculative Automatic parallelization is a promising strategy to improve appli- Speculative LRPD [22] R−LRPD [7] cation performance in the multicore era. However, common pro- Privateer (this work) gramming practices such as the reuse of data structures introduce Dynamic PD [21] artificial constraints that obstruct automatic parallelization. Privati- Polaris [29] ASSA [14] zation relieves these constraints by replicating data structures, thus Static Array Expansion [10] enabling scalable parallelization. Prior privatization schemes are Criterion DSA [31] RSSA [23] limited to arrays and scalar variables because they are sensitive to Privatization Manual Paralax [32] STMs [8, 18] the layout of dynamic data structures. This work presents Privateer, the first fully automatic privatization system to handle dynamic and Figure 1: Privatization Criterion and Memory Layout. recursive data structures, even in languages with unrestricted point- ers. To reduce sensitivity to memory layout, Privateer speculatively separates memory objects. Privateer’s lightweight runtime system contention and relaxes the program dependence structure by repli- validates speculative separation and speculative privatization to en- cating the reused storage locations, producing multiple copies in sure correct parallel execution. Privateer enables automatic paral- memory that support independent, concurrent access. Similarly, re- lelization of general-purpose C/C++ applications, yielding a ge- duction techniques relax ordering constraints on associative, com- omean whole-program speedup of 11.4× over best sequential ex- mutative operators by replacing (or expanding) storage locations.