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Speeding up Trilinos builds

Trilinos contains a lot of functionality. Build times can be significant. There are however different approaches to achieve speedups.

CMake configuration options

The simplest way to reduce overall build time is to disable unneeded targets. The output of the CMake invocation shows which packages were enabled and why they were enabled.

  • Unneeded packages should be disabled.

    Packages have required and optional dependencies on other packages. By enabling a package, e.g.

    -D Trilinos_ENABLE_MueLu:BOOL=ON

    all its required dependencies also get enabled. Optional dependencies get automatically enabled when

    -D Trilinos_ENABLE_ALL_OPTIONAL_PACKAGES:BOOL=ON

    which is the default behavior.

  • Depending on the package, building tests and examples can take significantly longer than the libraries themselves. Instead of enabling all tests or examples with

    -D Trilinos_ENABLE_TESTS:BOOL=ON \
-D Trilinos_ENABLE_EXAMPLES:BOOL=ON \

    one should prefer to only enable tests and examples for certain packages. For example, to enable tests and examples for the MueLu package one can set

    -D MueLu_ENABLE_TESTS:BOOL=ON \
-D MueLu_ENABLE_EXAMPLES:BOOL=ON \

  • Unneeded scalar types should be disabled. By default only double scalars are enabled.

  • Explicit template instantiation (ETI) is crucial for fast builds. It is enabled by default:

    -D Trilinos_ENABLE_EXPLICIT_INSTANTIATION:BOOL=ON

Ninja build system

The Ninja build system generator can be used as a replacement for the default UNIX Makefiles. It offers much faster dependency checking.

Install ninja:

  • Debian/Ubuntu: sudo apt-get install ninja-build
  • RedHat: sudo yum install ninja-build
  • MacOS: brew install ninja

and configure Trilinos with the CMake flag -G Ninja.

Trilinos will generate Makefiles in all sub-directories that call Ninja internally. This implies that make can still be used to build Trilinos. One difference is that instead of calling

make -j 10

we have to switch to

NP=10 make

to specify the level of build parallelism.

Ccache

Repeated build (e.g. in a CI pipeline or during development) can be sped up significantly by caching the results of compilation using ccache.

Install Ccache:

  • Debian/Ubuntu: sudo apt-get install ccache
  • RedHat: sudo yum install ccache
  • MacOS: brew install ccache

and configure Trilinos with the CMake flags

-D CMAKE_CXX_COMPILER_LAUNCHER:STRING="ccache" \
-D CMAKE_C_COMPILER_LAUNCHER:STRING="ccache"

Statistics about cache hits and misses can be displayed by calling

ccache --show-stats

This allows to verify that the build cache is being used.

When ccache is used in CI pipelines one has to make sure that the cache directory is preserved between subsequent runs.

Linker

If linker performance is an issue, it might make sense to explore alternative linkers such as LLVM's LLD or mold.