What is a CUDA Thread Block?

A thread block is a level of the CUDA programming model's thread hierarchy below a grid but above a thread . It is the CUDA programming model's abstract equivalent of the concrete cooperative thread arrays in PTX /SASS .

Blocks are the smallest unit of thread coordination exposed to programmers in the CUDA programming model . Blocks must execute independently, so that any execution order for blocks is valid, from fully serial in any order to all interleavings.

A single CUDA kernel launch produces one or more thread blocks (in the form of a thread block grid ), each of which contains one or more warps . Blocks can be arbitrarily sized, but they are typically multiples of the warp size (32 on all current CUDA GPUs).