Fix: CUDA Host-Side -O3 with CMake #562
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ax3l
added
bug
ax3l
commented
Jul 12, 2021
| list(TRANSFORM CMAKE_C_FLAGS_RELWITHDEBINFO REPLACE "-O2" "-O3") | ||
| list(TRANSFORM CMAKE_CXX_FLAGS_RELWITHDEBINFO REPLACE "-O2" "-O3") | ||
| # FIXME: due to the "AMReX inits CUDA first" logic we will first see this with -O2 in output | ||
| list(TRANSFORM CMAKE_CUDA_FLAGS_RELWITHDEBINFO REPLACE "-O2" "-O3") |
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This line was called before we set enable_language(cuda).
The result was an empty CUDA flag list, which as a result compiled the host with -O0 (GCC) and the device with -O3 (NVCC) for CUDA language translation units (TUs):
nvcc [no -O flags] [includes] [file].cpp
When calling cmake -S <src_dir> or ccmake again on the build directory, the CUDA language was enabled and then this was initialized correctly to -O3 ... for nvcc-compiled TUs.
`-O3` was only set for CUDA if we ran CMake at least twice. This was an intialization logic bug and should be set from the beginning, but we initialized CUDA too late / applied the transform too early. We now change the default build type to `Release` to avoid changing defaults and avoid further surprises. We will add optional `-g` for optimized builds again on a later PR.
SeverinDiederichs
approved these changes
Jul 13, 2021
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-O3was only set for CUDA if we ran CMake at least twice. This wasan intialization logic bug and should be set from the beginning, but
we initialized CUDA too late / applied the transform too early.
We now change the default build type to
Releaseto avoid changingdefaults and avoid further surprises.
We will add optional
-gfor optimized builds again on a later PR.Same as: ECP-WarpX/WarpX#2078 and similar implications as in #71. With the herein fixed issue for CUDA builds, the host-side default optimization was taken (GCC:
-O0but NVCC device-side is still defaulting to-O3). We saw ~30% performance regressions for GPU runs with WarpX with this unoptimized host code path for CUDA translation units.constisconst)