Grainsize64

Grainsize64 is a term used in parallel programming to denote a fixed granularity of work units, typically set to 64 elements or iterations. It is commonly implemented as a compile-time constant or a configurable parameter that groups portions of a workload into chunks that the scheduler can assign to threads.

In practice, a loop over a large data set is divided into consecutive chunks of 64 items, and each chunk is submitted as a separate task or scheduled as a unit of work. This approach aims to balance the overhead of task creation with the benefits of parallel execution, since too small a grain size can incur excessive scheduling overhead while too large a grain can hinder load balancing and cache efficiency.

The choice of 64 reflects a common compromise on many-core CPUs, aligning with typical cache line sizes and SIMD considerations, but the optimal value depends on the specific hardware, memory access patterns, and the overhead of the runtime. Some frameworks offer grain-size tuning or adaptive strategies, and grainsize64 may be used as a default or starting point in benchmarks or tutorials.

Variants such as grainsize32 or grainsize128 are used to explore different granularities. In benchmarking and performance tuning, practitioners compare results across grain sizes to identify the configuration that yields the best throughput and latency for a given workload.

See also: parallel programming, task scheduling, grain size, performance tuning.