Build '；cmake重建缓存&x27；对于*只是*子目录？

我对CMake的makefiles阶段的生成速度很慢有一个问题，类似于这个未回答的问题：

我的项目由一个顶级

CMakeLists.txt

文件组成，该文件使用

add_subdirectory（）

为单个库和可执行组件添加各种子项目

对于给定的组件，

CMakeLists.txt

文件包含如下内容：

add_library(mylib SHARED
  sourceFile1.cpp
  sourceFile2.cpp
  ...
)

我可以使用以下方法仅构建该目录的内容：

make mylib

如果我修改子目录中的

CMakeLists.txt

文件（作为从纯makefile迁移到CMake的一部分，我已经做了很多），然后运行

make

它会正确地重新运行CMake以更新配置，就像我运行

make rebuild\u cache

一样

但是，我注意到它实际上重新配置了整个项目。我真的希望CMake足够聪明，知道它只需要在当前目录和子目录中重新生成Makefile

有没有更好的方法来构建CMake项目来实现这一点？ 我看到一些人对每个子项目中的每个CMakeLists.txt使用project（）。总的来说，这是个好主意吗

或者/另外，是否有加快CMake生成步骤的方法？（目前我有60秒以上的版本）

如果您想讨论为什么CMake本身应该或不应该能够并行运行（想象一个

CMake-j

）

---

我已经添加了介子构建标签作为一个适度的奖励，但仅仅它还没有引起足够的注意来保证答案。正是这种问题可能导致人们将构建系统转换为介子构建（假设没有类似的问题）或类似的东西

正确答案可能是，如果不将源代码修改为CMake，则无法完成此操作。为了赢得赏金，我需要解释一下CMake的工作原理和/或它的缺陷

---

澄清：就我而言，生成步骤很慢。配置本身足够快，但在输出“-Configuring done”和“-Generating done”之间，CMake会挂起一段时间

对于完全缓存重建，我运行：

make -n rebuild_cache

如果编辑子目录中的单个CMakeLists.txt文件，以及 然后运行

make-n

，它将运行：

cd /home/project/cmake && /usr/local/bin/cmake -H/home/project/cmake -B/home/project/cmake --check-build-system CMakeFiles/Makefile.cmake 0

--检查生成系统是另一个未记录的选项

效果是一样的——重新生成整个构建系统，而不仅仅是当前子树。 源代码内构建和源代码外构建在行为上没有区别

如果我运行跟踪，例如：

strace -r cmake --trace -H/home/project/cmake -B/home/project/cmake 2>&1 | tee cmake_rebuild_cache.log
sort -r cmake_rebuild_cache.log | uniq

花费的大部分时间似乎都花在（或介于）打开、访问和取消链接的通话上

每项任务的长度都不尽相同，但它们的数量却在不断增加。 我不知道Labels.json和Labels.txt文件是关于什么的（CMake内部的东西）

一次运行：

49.363537 open("/home/projectbar/main/test/foo2bar/CMakeFiles/test2.foo2bar.testViewingSource1.dir/build.make", O_RDONLY) = 5 1.324777 access("/home/projectbar/main/test/performance/CMakeFiles/performancetest.chvcthulhu.testChvcthulhuPerformance2.dir", R_OK) = 0 0.907807 access("/home/projectbar/main/test/foo2bar/CMakeFiles/test2.foo2bar.testPeripheralConnection2.dir", R_OK) = 0 0.670272 unlink("/home/projectbar/main/src/foo2bar/Foo2Bar/CMakeFiles/foo2bar_lib.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.600272 access("/home/projectbar/main/test/foo2bar/testFilesModel2.ok", R_OK) = 0 0.599010 access("/home/projectbar/main/test/hve2snafu/testInvalidByte2c.ok", R_OK) = 0 0.582466 read(5, "openjdk version \"1.8.0_71\"\nOpenJ"..., 1024) = 130 0.570540 writev(3, [{"# CMAKE generated file: DO NOT E"..., 8190}, {"M", 1}], 2) = 8191 0.553576 close(4) = 0 0.448811 unlink("/home/projectbar/main/test/snafu2hve/CMakeFiles/test2.snafu2hve.testNoProbes2.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.431559 access("/home/projectbar/main/src/foo2bar/Foo2Bar/CMakeFiles/foo2bar_lib.dir", R_OK) = 0 0.408003 unlink("/home/projectbar/main/test/lachesis/CMakeFiles/test2.lachesis.testBadSequenceNumber1.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.407120 write(4, "# The set of languages for which"..., 566) = 566 0.406674 write(3, "# CMAKE generated file: DO NOT E"..., 675) = 675 0.383892 read(3, "ewingPeriod.cpp.o -c /home/bruce"..., 8191) = 8191 0.358490 unlink("/home/projectbar/main/cmake/CMakeFiles/mklinks.chvdiff.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 及

有待解决。这个问题实际上是关于为什么Makefile生成器很慢。我不确定忍者表演中的问题是有用的提示还是转移注意力

---

使用更多优化构建CMake没有帮助

根据我的跟踪输出和时间的输出，它不太可能出现。 用户时间以及在CMake代码中花费的时间都非常少。 （参见示例）

以下是我为完整性所做的尝试：

export CXX_FLAGS="-O3 -ftree-vectorise -msse2"
cmake -DCMAKE_BUILD_TYPE=RELEASE

实际上，使用更优化的CMake确实可以加快配置部分的速度， 但是在我的例子中，生成部分速度很慢。 从时序上看，这一步似乎受到了某种程度的I/O限制

---

我决定调查Florian的想法，即在文件流中使用内存来存储临时文件可能会有所不同

我决定尝试一下简单的方法，并让CMake将.tmp文件写入RAM磁盘

然后我全力以赴，尝试在RAM磁盘上生成构建系统：

sudo mkdir /mnt/ramdisk
sudo mount -t tmpfs -o size=512m tmpfs /mnt/ramdisk
/usr/bin/time -p cmake -H/<source> -B/mnt/ramdisk/build

与RAMF类似：

real 51.09
user 1.58
sys 0.50

这里会发生什么？我在猜测子进程，但我无法确定哪些子进程占用了挂钟时间（如果有的话）。它们看起来寿命很短

---

为了完整起见，这里是perf的一些输出（使用

-fno省略帧指针构建的CMake）

：

perf record-g——调用图dwarf-cmake-H-B
性能报告-g图

样本：17K事件“周期”，事件计数（约）：1436392067 子级自命令共享对象符号 +65.23%0.00%cmake cmake[.]do_cmake +65.02%0.00%cmake cmake[.]cmake:：运行 +60.32%0.00%cmake cmake[.]主要 +59.82%0.00%cmake libc-2.17.so[.]\u libc\u start\u main +57.78%0.00%cmake cmake[.]\u开始 +55.04%0.00%cmake cmake[.]cmGlobalUnixMakefileGenerator3:：Generate +54.56%0.00%cmake cmake[.]cmake:：生成 +49.90%0.00%cmake cmake[.]cmGlobalGenerator:：Generate +38.87%0.02%cmake cmake[.]cmLocalUnixMakefileGenerator3:：Generate +18.65%0.01%cmake cmake[.]CmakeFileTargetGenerator:：WriteTargetBuildRules +17.05%0.02%cmake cmake[.]CmakeFile:：ExecuteCommand +16.99%0.01%cmake cmake[.]CmakeFile:：ReadListFile +16.84%0.01%cmake cmake[.]cmCommand:：InvokeInitialPass +16.79%0.00%cmake cmake[.]cmake文件：：配置 +14.71%0.00%cmake cmake 2.009451 unlink("/home/projectbar/main/cmake/CMakeFiles/mklinks.lachesis.dir/Labels.json") = -1 ENOENT (No such file or directory) ) = 20 ) = 19 1.300387 access("/home/projectbar/main/test/chvedit/CMakeFiles/test2.chvedit.tefooultiMatchFactoringEdit2.dir", R_OK) = 0 1.067957 access("/home/projectbar/main/test/chvedit/CMakeFiles/test2.chvedit.tefooultiMatchFactoringEdit2.dir", R_OK) = 0 ) = 1 0.885854 unlink("/home/projectbar/main/src/gorkyorks2bar/CMakeFiles/doxygen.correct.gorkyorks2bar.dir/Labels.json") = -1 ENOENT (No such file or directory) 0.854539 access("/home/projectbar/main/test/reportImpressions/ReportImpressions/CMakeFiles/testsuite1_reportImpressions.dir", R_OK) = 0 0.791741 unlink("/home/projectbar/main/cmake/CMakeFiles/mklinks.bar_models.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.659506 unlink("/home/projectbar/main/cmake/CMakeFiles/mklinks.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.647838 unlink("/home/projectbar/main/test/libyar/YarModels/CMakeFiles/testsuite1_yarmodels.dir/Labels.txt") = -1 ENOENT (No such file or directory) 0.620511 unlink("/home/projectbar/main/test/libyar/YarModels/CMakeFiles/testsuite1_yarmodels.dir/Labels.json") = -1 ENOENT (No such file or directory) 0.601942 unlink("/home/projectbar/main/cmake/CMakeFiles/mklinks.lachesis.dir/Labels.txt") = -1 ENOENT (No such file or directory) 0.591871 access("/home/projectbar/main/src/runbardemo/simple_demo/CMakeFiles", R_OK) = 0 0.582448 write(3, "CMAKE_PROGRESS_1 = \n\n", 21) = 21 0.536947 write(3, "CMAKE_PROGRESS_1 = \n\n", 21) = 21 0.499758 unlink("/home/projectbar/main/test/foo2bar/CMakeFiles/test2.foo2bar.testInputDirectory1.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.458120 unlink("/home/projectbar/main/test/yak2dcs/CMakeFiles/test2.yak2dcs.testsuite2.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.448104 unlink("/home/projectbar/main/test/reportImpressions/CMakeFiles/test2.reportImpressions.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.444344 access("/home/projectbar/main/src/bananas/CMakeFiles/bin.bananas.dir", R_OK) = 0 0.442685 unlink("/home/projectbar/main/test/rvedit/CMakeFiles/test2.rvedit.tefooissingOptionValue.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.425604 unlink("/home/projectbar/main/test/listdcs/CMakeFiles/test2.listdcs.testListCalls5.dir/progress.make.tmp") = -1 ENOENT (No such file or directory) 0.391163 access("/home/projectbar/main/src/siedit/CMakeFiles/siedit.dir", R_OK) = 0 0.362171 access("/home/projectbar/main/test/foo2bar/CMakeFiles/test2.foo2emma.testHowResults6.dir", R_OK) = 0

/usr/bin/time -p ninja rebuild_cache

ninja: warning: multiple rules generate ../src/ams2yar/ams2yar. builds involving this target will not be correct; continuing anyway [-w dupbuild=warn] ninja: warning: multiple rules generate ../src/vox/vox. builds involving this target will not be correct; continuing anyway [-w dupbuild=warn] ninja: warning: multiple rules generate ../src/bananas/bananas. builds involving this target will not be correct; continuing anyway [-w dupbuild=warn] ninja: warning: multiple rules generate ../src/fidlertypes2fidlerinfo/fidlertypes2fidlerinfo. builds involving this target will not be correct; continuing anyway [-w dupbuild=warn] ninja: warning: multiple rules generate ../src/mkrundir/mkrundir. builds involving this target will not be correct; continuing anyway [-w dupbuild=warn] ninja: warning: multiple rules generate ../src/runyar/runyar. builds involving this target will not be correct; continuing anyway [-w dupbuild=warn] ninja: warning: multiple rules generate ../src/runyardemo/runyardemo. builds involving this target will not be correct; continuing anyway [-w dupbuild=warn] [1/1] Running CMake to regenerate build system... Generator=Ninja -- FOO_VERSION: 01.02.03 -- Configuring done -- Generating done -- Build files have been written to: /home/project/cmake/build real 12.67 user 1.01 sys 0.31

ninja: warning: multiple rules generate ../src/runfoobardemo/runfoobardemo. builds involving this target will not be correct; continuing anyway [-w dupbuild=warn]

ninja: error: dependency cycle: ../src/foobar -> ../src/foobar/CMakeFiles/foobar -> ../src/ams2emma/foobar

export CXX_FLAGS="-O3 -ftree-vectorise -msse2"
cmake -DCMAKE_BUILD_TYPE=RELEASE

sudo mkdir /mnt/ramdisk
sudo mount -t tmpfs -o size=512m tmpfs /mnt/ramdisk
/usr/bin/time -p cmake -H/<source> -B/mnt/ramdisk/build

real 59.61
user 1.55
sys 0.62
>du -sh /mnt/ramdisk/build/
4.4M    /mnt/ramdisk/build/

real 51.09
user 1.58
sys 0.50

perf record -g --call-graph dwarf cmake -H<source> -B<build>
perf report -g graph

Samples: 17K of event 'cycles', Event count (approx.): 14363392067 Children Self Command Shared Object Symbol + 65.23% 0.00% cmake cmake [.] do_cmake + 65.02% 0.00% cmake cmake [.] cmake::Run + 60.32% 0.00% cmake cmake [.] main + 59.82% 0.00% cmake libc-2.17.so [.] __libc_start_main + 57.78% 0.00% cmake cmake [.] _start + 55.04% 0.00% cmake cmake [.] cmGlobalUnixMakefileGenerator3::Generate + 54.56% 0.00% cmake cmake [.] cmake::Generate + 49.90% 0.00% cmake cmake [.] cmGlobalGenerator::Generate + 38.87% 0.02% cmake cmake [.] cmLocalUnixMakefileGenerator3::Generate + 18.65% 0.01% cmake cmake [.] cmMakefileTargetGenerator::WriteTargetBuildRules + 17.05% 0.02% cmake cmake [.] cmMakefile::ExecuteCommand + 16.99% 0.01% cmake cmake [.] cmMakefile::ReadListFile + 16.84% 0.01% cmake cmake [.] cmCommand::InvokeInitialPass + 16.79% 0.00% cmake cmake [.] cmMakefile::Configure + 14.71% 0.00% cmake cmake [.] cmMakefile::ConfigureSubDirectory + 14.67% 0.05% cmake cmake [.] cmMacroHelperCommand::InvokeInitialPass + 14.27% 0.02% cmake cmake [.] cmMakefileUtilityTargetGenerator::WriteRuleFiles + 13.91% 0.00% cmake cmake [.] cmGlobalGenerator::Configure + 13.50% 0.05% cmake cmake [.] cmOutputConverter::Convert + 13.48% 0.00% cmake cmake [.] cmAddSubDirectoryCommand::InitialPass + 13.46% 0.00% cmake cmake [.] cmMakefile::AddSubDirectory + 12.91% 0.00% cmake cmake [.] cmGlobalUnixMakefileGenerator3::Configure + 12.82% 0.00% cmake cmake [.] cmake::ActualConfigure + 10.90% 0.00% cmake cmake [.] cmake::Configure + 10.55% 0.02% cmake cmake [.] cmMakefileTargetGenerator::WriteObjectRuleFiles + 10.35% 0.09% cmake cmake [.] cmLocalUnixMakefileGenerator3::WriteMakeRule + 9.76% 0.03% cmake cmake [.] cmMakefileTargetGenerator::WriteObjectBuildFile + 7.97% 0.00% cmake cmake [.] cmMakefileLibraryTargetGenerator::WriteRuleFiles + 7.93% 0.00% cmake cmake [.] cmMakefileExecutableTargetGenerator::WriteRuleFiles + 7.88% 0.00% cmake cmake [.] cmLocalUnixMakefileGenerator3::WriteLocalMakefile + 7.68% 0.02% cmake [kernel.kallsyms] [k] sysret_audit + 7.60% 0.05% cmake [kernel.kallsyms] [k] __audit_syscall_exit + 7.40% 0.08% cmake cmake [.] cmsys::SystemTools::CollapseFullPath + 2.86% cmake libc-2.17.so [.] _int_malloc + 2.15% cmake libc-2.17.so [.] __memcpy_ssse3_back + 2.11% cmake [kernel.kallsyms] [k] find_next_bit + 1.84% cmake libc-2.17.so [.] __memcmp_sse4_1 + 1.83% cmake libc-2.17.so [.] _int_free + 1.71% cmake libstdc++.so.6.0.20 [.] std::__ostream_insert > + 1.18% cmake libstdc++.so.6.0.20 [.] std::basic_string, std::allocator >::~basic_string + 1.13% cmake libc-2.17.so [.] malloc + 1.12% cmake cmake [.] cmOutputConverter::Shell__ArgumentNeedsQuotes + 1.11% cmake libstdc++.so.6.0.20 [.] std::string::compare + 1.08% cmake libc-2.17.so [.] __strlen_sse2_pminub + 1.05% cmake cmake [.] std::string::_S_construct + 1.04% cmake cmake [.] cmsys::SystemTools::ConvertToUnixSlashes + 0.97% cmake cmake [.] yy_get_previous_state + 0.87% cmake cmake [.] cmOutputConverter::Shell__GetArgument + 0.76% cmake libstdc++.so.6.0.20 [.] std::basic_filebuf >::xsputn + 0.75% cmake libstdc++.so.6.0.20 [.] std::string::size + 0.75% cmake cmake [.] cmOutputConverter::Shell__SkipMakeVariables + 0.74% cmake cmake [.] cmOutputConverter::Shell__CharNeedsQuotesOnUnix + 0.73% cmake [kernel.kallsyms] [k] mls_sid_to_context + 0.72% cmake libstdc++.so.6.0.20 [.] std::basic_string, std::allocator >::basic_string + 0.71% cmake cmake [.] cmOutputConverter::Shell__GetArgumentSize + 0.65% cmake libc-2.17.so [.] malloc_consolidate + 0.65% cmake [kernel.kallsyms] [k] mls_compute_context_len + 0.65% cmake cmake [.] cmOutputConverter::Shell__CharNeedsQuotes + 0.64% cmake cmake [.] cmSourceFileLocation::Matches + 0.58% cmake cmake [.] cmMakefile::ExpandVariablesInStringNew + 0.57% cmake cmake [.] std::__deque_buf_size + 0.56% cmake cmake [.] cmCommandArgument_yylex + 0.55% cmake cmake [.] std::vector >::size + 0.54% cmake cmake [.] cmsys::SystemTools::SplitPath + 0.51% cmake libstdc++.so.6.0.20 [.] std::basic_streambuf >::xsputn

$ time -p cmake -G "MSYS Makefiles" ..
[...]
real 43.93
user 0.00
sys 0.03

cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS="-O3" -G "MSYS Makefiles" ..

$ time -p /c/temp/cmake-3.2.2/MSYS32/bin/cmake.exe -G "MSYS Makefiles" ..
[...]
real 41.37
user 0.01
sys 0.04

$ time -p /c/temp/cmake-3.2.2/MSYS32/bin/cmake.exe -G "MSYS Makefiles" ..
[...]
real 20.98
user 0.00
sys 0.04

$ cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS="-march=native -m64 -Ofast  -flto" -G "MSYS Makefiles" ..

$ time -p /c/temp/cmake-3.2.2/MSYS64/bin/cmake.exe -G "MSYS Makefiles" ..
[...]
real 25.59
user 0.00
sys 0.04

$ time -p /c/temp/cmake-3.2.2/MSYS64/bin/cmake.exe -G "MSYS Makefiles" ..
[...]
real 6.95
user 0.00
sys 0.03

cmake_minimum_required(VERSION 3.0)

project(CMakeTest CXX)

#set_property(GLOBAL PROPERTY GLOBAL_DEPENDS_DEBUG_MODE 1)

set(_idx 1)

while (_idx LESS 100)
    math(EXPR _next_idx "${_idx} + 1")
    if (NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/lib${_idx}")
        file(MAKE_DIRECTORY "lib${_idx}")
        file(
            WRITE "lib${_idx}/lib${_idx}.h"
                "int lib${_idx}_func();"
        )
        file(
            WRITE "lib${_idx}/lib${_idx}.cc"
                "#include \"lib${_next_idx}.h\"\n"
                "int lib${_idx}_func() { return lib${_next_idx}_func(); }"
        )
        file(
            WRITE "lib${_idx}/CMakeLists.txt"
                "add_library(lib${_idx} \"lib${_idx}.cc\")\n"
                "target_link_libraries(lib${_idx} lib${_next_idx})\n"
                "target_include_directories(lib${_idx} PUBLIC \".\")"
        )
    endif()
    add_subdirectory("lib${_idx}")
    set(_idx "${_next_idx}")
endwhile()

if (NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/lib${_idx}")
    file(MAKE_DIRECTORY "lib${_idx}")
    file(
        WRITE "lib${_idx}/lib${_idx}.h"
            "int lib${_idx}_func();"
    )
    file(
        WRITE "lib${_idx}/lib${_idx}.cc"
            "int lib${_idx}_func() { return 0; }"
    )
    file(
        WRITE "lib${_idx}/CMakeLists.txt"
            "add_library(lib${_idx} \"lib${_idx}.cc\")\n"
            "target_include_directories(lib${_idx} PUBLIC \".\")"
    )
endif()
add_subdirectory("lib${_idx}")

if (NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/main.cc")
    file(
        WRITE "main.cc"
            "#include \"lib1.h\"\n"
            "int main() { return lib1_func(); }"
    )
endif()

add_executable(${PROJECT_NAME} "main.cc")
target_link_libraries(${PROJECT_NAME} lib1)

$ touch ../lib100/CMakeLists.txt
$ time -p cmake ..
-- Configuring done
-- Generating done
-- Build files have been written to: [your path here]
real 28.89
user 0.01
sys 0.04