| Name String |
| |
| cl_intel_required_subgroup_size |
| |
| Contributors |
| |
| Ben Ashbaugh, Intel |
| |
| Contact |
| |
| Ben Ashbaugh, Intel (ben.ashbaugh 'at' intel.com) |
| |
| Version |
| |
| Version 1, July 14, 2016 |
| |
| Number |
| |
| OpenCL Extension #43 |
| |
| Status |
| |
| Final Draft |
| |
| Dependencies |
| |
| Support for OpenCL 2.1, cl_khr_subgroups, or cl_intel_subgroups is required. |
| |
| This extension is written against revision 23 of the OpenCL 2.1 API |
| specification, against revision 30 of the OpenCL 2.0 OpenCL C specification, |
| against version 31 of the OpenCL 2.0 Extensions specification, and against |
| version 3 of the cl_intel_subgroups specification. |
| |
| Overview |
| |
| The goal of this extension is to allow programmers to optionally specify |
| the required subgroup size for a kernel function. This information is |
| important for the correctness of many subgroup algorithms, and in some cases |
| may be used by the compiler to generate more optimal code. |
| |
| New API Enums |
| |
| Accepted as the <param_name> parameter of clGetDeviceInfo: |
| |
| CL_DEVICE_SUB_GROUP_SIZES_INTEL 0x4108 |
| |
| Accepted as the <param_name> parameter of clGetKernelWorkGroupInfo: |
| |
| CL_KERNEL_SPILL_MEM_SIZE_INTEL 0x4109 |
| |
| Accepted as the <param_name> parameter of clGetKernelSubGroupInfo and/or |
| clGetKernelSubGroupInfoKHR: |
| |
| CL_KERNEL_COMPILE_SUB_GROUP_SIZE_INTEL 0x410A |
| |
| New OpenCL C Optional Attribute Qualifiers |
| |
| Optional __kernel qualifier: |
| |
| __attribute__((intel_reqd_sub_group_size(<int>))) |
| |
| Add to Table 4.3 - "OpenCL Device Queries": |
| |
| "-------------------------------------------------------------------------------------- |
| cl_device_info Return Type Description |
| ------------------------------- ----------- ---------------------------------------- |
| CL_DEVICE_SUB_GROUP_SIZES_INTEL size_t[] Returns the set of subgroup sizes |
| supported by the device. |
| --------------------------------------------------------------------------------------" |
| |
| Add to Table 5.21 - "clGetKernelWorkGroupInfo parameter queries": |
| |
| "-------------------------------------------------------------------------------------- |
| cl_kernel_work_group_info Return Type Description |
| ------------------------- ----------- ---------------------------------------------- |
| CL_KERNEL_SPILL_MEM_ cl_ulong Returns the amount of spill memory used by |
| SIZE_INTEL a kernel. The meaning of this value will |
| vary from implementation-to-implementation, |
| however a return value of 0 will always |
| indicate that compiler was able to compile |
| the kernel to fit into the device's register |
| file without spilling registers to memory. |
| --------------------------------------------------------------------------------------" |
| |
| Add to Table 5.22 - "clGetKernelSubGroupInfo parameter queries" in the OpenCL 2.1 API |
| spec, to the table in Section 9.17.2.1 for clGetKernelSubGroupInfoKHR in the OpenCL |
| 2.0 Extensions spec, and to the table describing the changes to Section 5.9.3 for |
| clGetKernelSubGroupInfoKHR in the cl_intel_subgroups spec: |
| |
| "-------------------------------------------------------------------------------------- |
| cl_kernel_sub_group_info Input Type Return Type Description |
| ------------------------ ---------- ----------- ----------------------------------- |
| CL_KERNEL_COMPILE_ ignored size_t Returns the subgroup size specified |
| SUB_GROUP_SIZE_INTEL by the __attribute__(( |
| intel_reqd_sub_group_size(<int>))) |
| qualifier. Refer to section 6.7.2. |
| |
| If the subgroup size is not |
| specified using the above attribute |
| qualifier then 0 is returned. |
| --------------------------------------------------------------------------------------" |
| |
| Add to Section 6.7.2 - "Optional Attribute Qualifiers" |
| |
| "The optional __attribute__((intel_reqd_sub_group_size(<int>))) can be used to indicate |
| that the kernel must be compiled and executed with the specified subgroup size. When |
| this attribute is present, get_max_sub_group_size() is guaranteed to return the |
| specified integer value. This is important for the correctness of many subgroup |
| algorithms, and in some cases may be used by the compiler to generate more optimal |
| code. |
| |
| Note that there is no guarantee for the value of get_sub_group_size() even when this |
| attribute is present, particularly when the work-group size is not evenly divisible by |
| the required subgroup size. |
| |
| Note as well that some devices may support a limited number of subgroup sizes, and |
| that some devices may not support all language constructs with all subgroup sizes. |
| This means that some kernels may fail compilation with one required subgroup size and |
| succeed with another required subgroup size, even if both subgroup sizes are supported |
| by the device. |
| |
| Finally, note that requiring one subgroup size (particularly, a larger subgroup size) |
| may require more spill memory than another subgroup size, and may negatively impact |
| application performance." |
| |
| Revision History |
| |
| Version 1 - Initial Revision |
| |
