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GPU: make the kernel entry-point signature work on Metal #15895

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9 changes: 9 additions & 0 deletions GPU/Common/GPUCommonDefAPI.h
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Original file line number Diff line number Diff line change
Expand Up @@ -277,6 +277,15 @@
#define get_group_id(dim) (blockIdx.x)
#elif defined(__OPENCL__)
// Using OpenCL defaults
#elif defined(__METAL__)
// MSL has no work-item builtins; these come in as kernel attributes, declared
// by GPUCA_KRNL_GRID_ARGS on every entry point.
#define get_global_id(dim) (_metalTgIg * _metalTPerTg + _metalTiTg)
#define get_global_size(dim) (_metalTPerTg * _metalTgPerG)
#define get_num_groups(dim) (_metalTgPerG)
#define get_local_id(dim) (_metalTiTg)
#define get_local_size(dim) (_metalTPerTg)
#define get_group_id(dim) (_metalTgIg)
#else
#define get_global_id(dim) iBlock
#define get_global_size(dim) nBlocks
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11 changes: 10 additions & 1 deletion GPU/GPUTracking/Base/GPUReconstructionKernelMacros.h
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Expand Up @@ -63,8 +63,17 @@
#define GPUCA_ATTRRES(...) GPUCA_M_EXPAND(GPUCA_M_CAT(GPUCA_ATTRRES_, GPUCA_M_FIRST(__VA_ARGS__)))(__VA_ARGS__)

// GPU Kernel entry point
// MSL requires every kernel parameter to carry an attribute, and supplies the
// grid dimensions the same way, so the backend gets to shape both ends of the
// parameter list.
#ifndef GPUCA_KRNL_SECTOR_ARG
#define GPUCA_KRNL_SECTOR_ARG int32_t _iSector_internal

@davidrohr davidrohr Oct 8, 2026

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I don't understand why you need a special treatment for the sector variable in metal?
The sector variable is a normal variable, which is passed in like any other parameter to function calls.

#endif
#ifndef GPUCA_KRNL_GRID_ARGS
#define GPUCA_KRNL_GRID_ARGS
#endif
#define GPUCA_KRNLGPU_DEF(x_class, x_attributes, x_arguments, ...) \
GPUg() void GPUCA_ATTRRES(GPUCA_M_STRIP(x_attributes)) GPUCA_M_CAT(krnl_, GPUCA_M_KRNL_NAME(x_class))(GPUCA_CONSMEM_PTR int32_t _iSector_internal GPUCA_M_STRIP(x_arguments))
GPUg() void GPUCA_ATTRRES(GPUCA_M_STRIP(x_attributes)) GPUCA_M_CAT(krnl_, GPUCA_M_KRNL_NAME(x_class))(GPUCA_CONSMEM_PTR GPUCA_KRNL_SECTOR_ARG GPUCA_M_STRIP(x_arguments) GPUCA_KRNL_GRID_ARGS)

@davidrohr davidrohr Oct 8, 2026

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Hm, but this means that you pass in local and global id and size as argument to the kernel function.
However, in OpenCL / CUDA / HIP, these varaibles are available everywhere, without being passed in.
I.e., they are also available in subfunctions. And I don't want to pass them in explicitly to each place where they are used. Is this somehow possible with metal?


#ifdef GPUCA_KRNL_DEFONLY
#define GPUCA_KRNLGPU(...) GPUCA_KRNLGPU_DEF(__VA_ARGS__);
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10 changes: 10 additions & 0 deletions GPU/GPUTracking/Base/metal/GPUReconstructionMETAL.metal
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Expand Up @@ -70,6 +70,16 @@ using namespace metal;
device char* pConstantRaw [[buffer(1)]],
#define GPUCA_CONSMEM (*(device GPUConstantMem*)pConstantRaw)

// Every kernel parameter needs an attribute, so the sector index arrives as a
// buffer rather than by value, and the grid dimensions come in at the end, where
// GPUCommonDefAPI.h's get_group_id() and friends pick them up.
#define GPUCA_KRNL_SECTOR_ARG constant int32_t& _iSector_internal [[buffer(2)]]
#define GPUCA_KRNL_GRID_ARGS \
, uint _metalTgIg [[threadgroup_position_in_grid]] \
, uint _metalTiTg [[thread_position_in_threadgroup]] \
, uint _metalTPerTg [[threads_per_threadgroup]] \
, uint _metalTgPerG [[threadgroups_per_grid]]

#include "GPUReconstructionKernelList.h"

// clang-format on
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