clGetKernelWorkGroupInfo
clGetKernelWorkGroupInfo
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clGetKernelWorkGroupInfo Returns information about the kernel object that may be specific to a device.

##

cl_int `clGetKernelWorkGroupInfo` cl_kernel kernel cl_device_id device cl_kernel_work_group_info param_name size_t param_value_size void *param_value size_t *param_value_size_ret

## Parameters

`kernel`

  Specifies the kernel object being queried.

`device`

  Identifies a specific device in the list of devices associated with `kernel`. The list of devices is the list of devices in the OpenCL context that is associated with `kernel`. If the list of devices associated with `kernel` is a single device, `device` can be a NULL value.

`param_name`

  Specifies the information to query. The list of supported `param_name` types and the information returned in `param_value` by `clGetKernelWorkGroupInfo` is described in the table below.

`param_value`

  A pointer to memory where the appropriate result being queried is returned. If `param_value` is NULL, it is ignored.

`param_value_size`

  Used to specify the size in bytes of memory pointed to by `param_value`. This size must be ≥ size of return type as described in the table below.

  cl_kernel_work_group_info | Return Type | Info. returned in `param_value`
  --- | --- | ---
  `CL_KERNEL_GLOBAL_WORK_SIZE` | size_t[3] | This provides a mechanism for the application to query the maximum global size that can be used to execute a kernel (i.e. `global_work_size` argument to clEnqueueNDRangeKernel) on a custom device given by `device` or a built-in kernel on an OpenCL device given by `device`. If `device` is not a custom device or `kernel` is not a built-in kernel, clGetKernelArgInfo returns the error `CL_INVALID_VALUE`.
  `CL_KERNEL_WORK_GROUP_SIZE` | size_t | This provides a mechanism for the application to query the maximum work-group size that can be used to execute a kernel on a specific device given by `device`. The OpenCL implementation uses the resource requirements of the kernel (register usage etc.) to determine what this work-group size should be.
  `CL_KERNEL_COMPILE_- WORK_GROUP_SIZE` | size_t[3] | Returns the work-group size specified by the `__attribute__((reqd_work_group_size(X, Y, Z)))` qualifier. See Function Qualifiers. If the work-group size is not specified using the above attribute qualifier (0, 0, 0) is returned.
  `CL_KERNEL_LOCAL_MEM_SIZE` | cl_ulong | Returns the amount of local memory in bytes being used by a kernel. This includes local memory that may be needed by an implementation to execute the kernel, variables declared inside the kernel with the __local address qualifier and local memory to be allocated for arguments to the kernel declared as pointers with the __local address qualifier and whose size is specified with clSetKernelArg. If the local memory size, for any pointer argument to the kernel declared with the __local address qualifier, is not specified, its size is assumed to be 0.
  `CL_KERNEL_PREFERRED_WORK_- GROUP_SIZE_MULTIPLE` | size_t | Returns the preferred multiple of workgroup size for launch. This is a performance hint. Specifying a workgroup size that is not a multiple of the value returned by this query as the value of the local work size argument to clEnqueueNDRangeKernelwill not fail to enqueue the kernel for execution unless the work-group size specified is larger than the device maximum.
  `CL_KERNEL_PRIVATE_MEM_SIZE` | cl_ulong | Returns the minimum amount of private memory, in bytes, used by each workitem in the kernel. This value may include any private memory needed by an implementation to execute the kernel, including that used by the language built-ins and variable declared inside the kernel with the __private qualifier.

`param_value_size_ret`

  Returns the actual size in bytes of data copied to `param_value`. If `param_value_size_ret` is NULL, it is ignored.

## Errors

Returns CL_SUCCESS if the function is executed successfully. Otherwise, it returns one of the following errors:

- CL_INVALID_DEVICE if `device` is not in the list of devices associated with `kernel` or if `device` is NULL but there is more than one device associated with `kernel`.
- CL_INVALID_VALUE if `param_name` is not valid, or if size in bytes specified by `param_value_size` is < size of return type as described in the table above and `param_value` is not NULL.
- CL_INVALID_VALUE if `param_name` is `CL_KERNEL_GLOBAL_WORK_SIZE` and `device` is not a custom device or `kernel` is not a built-in kernel.
- CL_INVALID_KERNEL if `kernel` is a not a valid kernel object.
- CL_OUT_OF_RESOURCES if there is a failure to allocate resources required by the OpenCL implementation on the device.
- CL_OUT_OF_HOST_MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.

## Specification

OpenCL Specification

## Also see

clCreateKernel, clCreateKernelsInProgram, clReleaseKernel, clRetainKernel, clSetKernelArg, clGetKernelInfo

##