Runtime selection of libCEED backends allows users to use CPU backends for easier debugging. Code that produces correct results with CPU backends will produce correct results on GPU backends, provided that JiT and memory access assumptions of the libCEED API are respected.
The filepath to the user source code is passed in
CeedQFunctionCreateInterior() as the
This filepath should typically be an absolute path to ensure the JiT compilation can locate the source file.
The filepath may also be relative to a root directory set with
CEED_QFUNCTION macro automatically creates a string with the absolute path stored in the variable
user_loc for a
The entire contents of this file and all locally included files (
#include "foo.h") are used during JiT compilation for GPU backends.
Installed headers (
#include <bar.h>) are omitted in the source code passed to JiT, but the compilation environment may supply common headers such as
These source file must only contain syntax constructs supported by C99 and all targeted backends (i.e. CUDA for
/gpu/cuda, OpenCL/SYCL for
All source files must be at the provided filepath at runtime for JiT to function.
GPU backends require stricter adherence to memory access assumptions, but CPU backends may occasionally report correct results despite violations of memory access assumptions.
CeedQFunctionContext have read-only and read-write accessors, and
CeedVector allow write-only access.
Read-only access of
CeedQFunctionContext memory spaces must be respected for proper GPU behavior.
Write-only access of
CeedVector memory spaces asserts that all data in the
CeedVector is invalid until overwritten.
CeedQFunction assume that all input arrays are read-only and all output arrays are write-only and the
CeedQFunctionUser must adhere to these assumptions, only reading data in the input arrays and fully overwriting the output arrays.
CeedQFunctionUser have read-write access for
CeedQFunctionContext data, unless
CeedQFunctionSetContextWritable() was used to indicate that read-only access is sufficient.
/cpu/self/memcheck backends explicitly verify read-only and write-only memory access assumptions.