GpuKernelLaunch¶
Launches a GPU kernel.
Declaration¶
Syntax¶
GpuKernelLaunch(symbol kernel, expr grid_size, expr block_size,
call_arg* args)
Arguments¶
Argument |
Description |
|---|---|
|
the Function to run. Its signature has |
|
the number of blocks to launch. |
|
the number of threads per block. |
|
the arguments passed to every thread. |
Return values¶
None.
Description¶
A launch is not a call: it starts grid_size * block_size threads and, unless
the backend says otherwise, returns without waiting for them.
GpuSync is what waits.
The execution configuration is part of the node rather than of the kernel, because the same kernel is normally launched with different sizes.
The kernel is an ordinary Function; what makes
it launchable is that its signature has exec_space = Kernel, and a kernel
has no result. See exec_space.
The gpu_offload pass replaces a parallel loop assigned to the device with its
launch, together with the copies the host makes before and after it; nothing
of the original loop is kept. gpu_kernel_finalize records the kernel’s
Function.gpu layout after shared lowering. device_launch_expand and both
device emitters consume that layout. Workspace sizes are evaluated once on the host and passed as
explicit scalar arguments, so host allocation and device indexing use the
same values.
Before creating a launch, GPU offload checks the allocation of allocatable array results in callees that remain out of line. Nested or multiple allocation sites must agree with a buffer shape established by an unconditional fixed allocation. Otherwise the loop is rejected while the original loop is still available, which is an error: it is a lowering LFortran does not have yet. Reallocation and conditional assignments remain eligible when they preserve every extent, not just the total element count.
A loop reaches GPU offload only after the unsupported-construct check in the
parallel_dispatch pass has assigned it to the device (see
GPU offloading), so a loop the offload cannot
lower is a compile-time error, whatever its reason, whether or not
--gpu-allow-cpu-fallback is given, and also with --show-gpu-kernel-source.
Examples¶
(GpuKernelLaunch
:kernel (SymbolRef 1 "zero")
:grid_size (IntegerConstant
:n 1
:type (Integer
:kind 4
)
:intboz_type :Decimal
)
:block_size (IntegerConstant
:n 256
:type (Integer
:kind 4
)
:intboz_type :Decimal
)
:args [
(call_arg
:value (Var
:v (SymbolRef 2 "a")
)
)
]
)
It comes from this complete ASR text document:
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(GpuKernelLaunch
:kernel (SymbolRef 1 "zero")
:grid_size (IntegerConstant
:n 1
:type (Integer
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:intboz_type :Decimal
)
:block_size (IntegerConstant
:n 256
:type (Integer
:kind 4
)
:intboz_type :Decimal
)
:args [
(call_arg
:value (Var
:v (SymbolRef 2 "a")
)
)
]
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(GpuSync)
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