4.7. Occupancy

This section describes the occupancy calculation functions of the CUDA runtime application programming interface.

Besides the occupancy calculator functions (cudaOccupancyMaxActiveBlocksPerMultiprocessor and cudaOccupancyMaxActiveBlocksPerMultiprocessorWithFlags), there are also C++ only occupancy-based launch configuration functions documented in C++ API Routines module.

See cudaOccupancyMaxPotentialBlockSize ( C++ API), cudaOccupancyMaxPotentialBlockSize ( C++ API), cudaOccupancyMaxPotentialBlockSizeVariableSMem ( C++ API), cudaOccupancyMaxPotentialBlockSizeVariableSMem ( C++ API)

Functions

__host__ ​ __device__ ​cudaError_t cudaOccupancyMaxActiveBlocksPerMultiprocessor ( int* numBlocks, const void* func, int  blockSize, size_t dynamicSMemSize )
Returns occupancy for a device function.
__host__ ​cudaError_t cudaOccupancyMaxActiveBlocksPerMultiprocessorWithFlags ( int* numBlocks, const void* func, int  blockSize, size_t dynamicSMemSize, unsigned int  flags )
Returns occupancy for a device function with the specified flags.

Functions

__host__ ​ __device__ ​cudaError_t cudaOccupancyMaxActiveBlocksPerMultiprocessor ( int* numBlocks, const void* func, int  blockSize, size_t dynamicSMemSize )
Returns occupancy for a device function.
Parameters
numBlocks
- Returned occupancy
func
- Kernel function for which occupancy is calculated
blockSize
- Block size the kernel is intended to be launched with
dynamicSMemSize
- Per-block dynamic shared memory usage intended, in bytes
Returns

cudaSuccess, cudaErrorCudartUnloading, cudaErrorInitializationError, cudaErrorInvalidDevice, cudaErrorInvalidDeviceFunction, cudaErrorInvalidValue, cudaErrorUnknown,

Description

Returns in *numBlocks the maximum number of active blocks per streaming multiprocessor for the device function.

Note:

Note that this function may also return error codes from previous, asynchronous launches.

See also:

cudaOccupancyMaxActiveBlocksPerMultiprocessorWithFlags, cudaOccupancyMaxPotentialBlockSize ( C++ API), cudaOccupancyMaxPotentialBlockSizeWithFlags ( C++ API), cudaOccupancyMaxPotentialBlockSizeVariableSMem ( C++ API), cudaOccupancyMaxPotentialBlockSizeVariableSMemWithFlags ( C++ API), cuOccupancyMaxActiveBlocksPerMultiprocessor

__host__ ​cudaError_t cudaOccupancyMaxActiveBlocksPerMultiprocessorWithFlags ( int* numBlocks, const void* func, int  blockSize, size_t dynamicSMemSize, unsigned int  flags )
Returns occupancy for a device function with the specified flags.
Parameters
numBlocks
- Returned occupancy
func
- Kernel function for which occupancy is calculated
blockSize
- Block size the kernel is intended to be launched with
dynamicSMemSize
- Per-block dynamic shared memory usage intended, in bytes
flags
- Requested behavior for the occupancy calculator
Returns

cudaSuccess, cudaErrorCudartUnloading, cudaErrorInitializationError, cudaErrorInvalidDevice, cudaErrorInvalidDeviceFunction, cudaErrorInvalidValue, cudaErrorUnknown,

Description

Returns in *numBlocks the maximum number of active blocks per streaming multiprocessor for the device function.

The flags parameter controls how special cases are handled. Valid flags include:

  • cudaOccupancyDisableCachingOverride: This flag suppresses the default behavior on platform where global caching affects occupancy. On such platforms, if caching is enabled, but per-block SM resource usage would result in zero occupancy, the occupancy calculator will calculate the occupancy as if caching is disabled. Setting this flag makes the occupancy calculator to return 0 in such cases. More information can be found about this feature in the "Unified L1/Texture Cache" section of the Maxwell tuning guide.

Note:

Note that this function may also return error codes from previous, asynchronous launches.

See also:

cudaOccupancyMaxActiveBlocksPerMultiprocessor, cudaOccupancyMaxPotentialBlockSize ( C++ API), cudaOccupancyMaxPotentialBlockSizeWithFlags ( C++ API), cudaOccupancyMaxPotentialBlockSizeVariableSMem ( C++ API), cudaOccupancyMaxPotentialBlockSizeVariableSMemWithFlags ( C++ API), cuOccupancyMaxActiveBlocksPerMultiprocessorWithFlags