Atomics Application Binary Interface

The mappings of programming languages’ atomic operations to the PTX ISA need to be implemented in a consistent manner across all programming languages that may concurrently access shared memory. The mapping from C++11 atomics for the CUDA architecture are proven correct in A Formal Analysis of the NVIDIA PTX Memory Consistency Model. The PTX ISA provides atomic memory operations and fences for acquire, release, acquire-release, and relaxed C++ memory ordering semantics.

Note

The memory order parameter is monotonic, and so it is valid to strengthen any such parameter. For example, it is valid to strengthen fence.sc.<scope>; ld.relaxed.<scope>; to fence.sc.<scope>; ld.acquire.<scope>; for sequentially consistent loads. The same applies for all mappings below.

Note

Where there is a choice of PTX ABI ISA mapping for a given C, C++, or CUDA C++ API it is acceptable to pick either and to mix mappings within the same binary.

The PTX ABI for C++ sequentially consistent atomic operations is the following:

C or C++ or CUDA C++ API	PTX ABI ISA mapping
atomic_thread_fence(memory_order_seq_cst, thread_scope_<scope>)	fence.sc.<scope>;
atomic_load(memory_order_seq_cst, thread_scope_<scope>)	fence.sc.<scope>; ld.acquire.<scope>; (recommended) OR fence.sc.<scope>; ld.relaxed.<scope>; fence.acquire.<scope>;
atomic_store(memory_order_seq_cst, thread_scope_<scope>)	fence.sc.<scope>; st.relaxed.<scope>;
atomic_<rmw op>(memory_order_seq_cst, thread_scope_<scope>)	fence.sc.<scope>; atom.acquire.<scope>.<rmw op>; (recommended) OR fence.sc.<scope>; atom.relaxed.<scope>.<rmw op>; fence.acquire.<scope>;

The PTX ABI for C++ release atomic operations is the following:

C or C++ or CUDA C++ API	PTX ABI ISA mapping
atomic_thread_fence(memory_order_release, thread_scope_<scope>)	fence.release.<scope>;
atomic_store(memory_order_release, thread_scope_<scope>)	st.release.<scope>; (recommended) OR fence.release.<scope>; st.relaxed.<scope>;
atomic_<rmw op>(memory_order_release, thread_scope_<scope>)	atom.release.<scope>.<rmw op>; (recommended) OR fence.release.<scope>; atom.relaxed.<scope>.<rmw op>;

The PTX ABI for C++ acquire atomic operations is the following:

C or C++ or CUDA C++ API	PTX ABI ISA mapping
atomic_thread_fence(memory_order_acquire, thread_scope_<scope>)	fence.acquire.<scope>;
atomic_load(memory_order_acquire, thread_scope_<scope>)	ld.acquire.<scope>; (recommended) OR ld.relaxed.<scope>; fence.acquire.<scope>;
atomic_<rmw op>(memory_order_acquire, thread_scope_<scope>)	atom.acquire.<scope>.<rmw op>; (recommended) OR atom.relaxed.<scope>.<rmw op>; fence.acquire.<scope>;

The PTX ABI for C++ acquire-release atomic operations is the following:

C or C++ or CUDA C++ API	PTX ABI ISA mapping
atomic_thread_fence(memory_order_acq_rel, thread_scope_<scope>)	fence.acq_rel.<scope>;
atomic_<rmw op>(memory_order_acq_rel, thread_scope_<scope>)	atom.acq_rel.<scope>.<rmw op>; (recommended) OR fence.release.<scope>; atom.acquire.<scope>.<rmw op>; OR fence.release.<scope>; atom.relaxed.<scope>.<rmw op>; fence.acquire.<scope>;

The PTX ABI for C++ relaxed atomic operations is the following:

C or C++ or CUDA C++ API	PTX ABI ISA mapping
atomic_load(memory_order_relaxed, thread_scope_<scope>)	ld.relaxed.<scope>;
atomic_store(memory_order_relaxed, thread_scope_<scope>)	st.relaxed.<scope>;
atomic_<rmw op>(memory_order_relaxed, thread_scope_<scope>)	atom.relaxed.<scope>.<rmw op>;