[CMake] Parallel build setup question

[Konstantin Tokarev]

16.02.2018, 21:32, "Cornelis Bockemühl" <cornelis at bockemuehl.ch>:
> Thanks - that did the trick!
>
> And indeed by entering -j4 in the "Tool arguments" field, the build command changes "magically" into "cmake --build . --target all -- -j4" - with the "--" to pass the argument further to gmake.
>
> Actually compile time of my project after a "clean" went down from 23 to 14 min, thus reduction factor 1.6 with 4 processors: I tend to attribute the diffference to "almost 4" to the nature of my project where gmake seems not to see too many opportunities for parallel processing. Maybe it works always module by module, or whatever.
>
> Anyway, my question is answered - thanks again!

Note that if you used Ninja generator, it would use all cores by default.

>
> Regards,
> Cornelis
>
> Am Freitag, den 16.02.2018, 20:25 +0300 schrieb Konstantin Tokarev:
>> 16.02.2018, 20:20, "Cornelis Bockemühl" <cornelis at bockemuehl.ch>:
>>> Thanks for your hints! And you are right: it is still interesting to know how QtCreator is actually invoking and using cmake.
>>
>> You should go to project settings and change cmake --build arguments there
>>
>>> This is the beginning of a log that the QtCreator was generating during a build. Actually with two modules where nothing had to be done, but still showing how cmake and gmake are being invoked - and all a bit above my understanding of the two tools:
>>>
>>> ===================================
>>> /usr/bin/cmake -H/Sources/GitLinux/RMT -B/BinariesLinux/RMT/Debug --check-build-system CMakeFiles/Makefile.cmake 0
>>> /usr/bin/cmake -E cmake_progress_start /BinariesLinux/RMT/Debug/CMakeFiles /BinariesLinux/RMT/Debug/CMakeFiles/progress.marks
>>> /usr/bin/gmake -f CMakeFiles/Makefile2 all
>>> gmake[1]: Entering directory '/BinariesLinux/RMT/Debug'
>>> /usr/bin/gmake -f CMakeFiles/FirstModule.dir/build.make CMakeFiles/FirstModule.dir/depend
>>> gmake[2]: Entering directory '/BinariesLinux/RMT/Debug'
>>> cd /BinariesLinux/RMT/Debug && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /Sources/GitLinux/RMT /Sources/GitLinux/RMT /BinariesLinux/RMT/Debug /BinariesLinux/RMT/Debug /BinariesLinux/RMT/Debug/CMakeFiles/FirstModule.dir/DependInfo.cmake --color=
>>> gmake[2]: Leaving directory '/BinariesLinux/RMT/Debug'
>>> /usr/bin/gmake -f CMakeFiles/FirstModule.dir/build.make CMakeFiles/FirstModule.dir/build
>>> gmake[2]: Entering directory '/BinariesLinux/RMT/Debug'
>>> gmake[2]: Nothing to be done for 'CMakeFiles/FirstModule.dir/build'.
>>> gmake[2]: Leaving directory '/BinariesLinux/RMT/Debug'
>>> [  3%] Built target FirstModule
>>> /usr/bin/gmake -f CMakeFiles/SecondModule.dir/build.make CMakeFiles/SecondModule.dir/depend
>>> gmake[2]: Entering directory '/BinariesLinux/RMT/Debug'
>>> cd /BinariesLinux/RMT/Debug && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /Sources/GitLinux/RMT /Sources/GitLinux/RMT /BinariesLinux/RMT/Debug /BinariesLinux/RMT/Debug /BinariesLinux/RMT/Debug/CMakeFiles/SecondModule.dir/DependInfo.cmake --color=
>>> gmake[2]: Leaving directory '/BinariesLinux/RMT/Debug'
>>> /usr/bin/gmake -f CMakeFiles/SecondModule.dir/build.make CMakeFiles/SecondModule.dir/build
>>> gmake[2]: Entering directory '/BinariesLinux/RMT/Debug'
>>> gmake[2]: Nothing to be done for 'CMakeFiles/SecondModule.dir/build'.
>>> gmake[2]: Leaving directory '/BinariesLinux/RMT/Debug'
>>> [  6%] Built target SecondModule
>>> ...
>>> ===========================================
>>>
>>> For example I do not really understand all the parameters that are passed to cmake - and I do not find them in the documentation either (like -H, -B or --check-build-system...
>>>
>>> Regards,
>>> Cornelis
>>>
>>> Am Freitag, den 16.02.2018, 08:59 -0800 schrieb Michael Ellery:
>>>> I don’t know anything about QTCreator, but the question really boils down to how to get your IDE to pass extra args to the build tool - it’s not really a cmake issue except to the extent that CMake can be used to invoke the build step (after it has been used to generate the build). It sounds like QT uses “cmake --build” to do the build phase (which makes sense), so you just need to add your “-j N” argument to the build step invocation. If you believe this: https://doc.qt.io/qtcreator/creator-build-settings.html, then it sounds like maybe “Tool Arguments” is what you want (see “CMake Build Steps”) ? BTW, the way I do this myself (since I don’t use an IDE) is something like “cmake --build . -- -j 8” where the double dash stops shell argument processing and effectively passes everything else on to the build tool that cmake ultimately invokes (e.g. make or ninja or msbuild, etc.) HTH, Mike On Feb 16, 2018, at 8:31 AM, Cornelis Bockemühl <cornelis at bockemuehl.ch> wrote: Hello, Somehow I seem to miss some crucial point regarding setup for parallel build with CMake, so I would be happy if somebody can push me the last few millimeters to hit my target! My configuration is on OpenSuse Linux (Leap - 64-bit), working with QtCreator and CMake, using the "make" configuration. I learned from "the internet" that actually I would have to pass a -jN option to make or gmake (with N being the max number of processors I want to use). Or even more elegant: go for a -lN option to somehow balance the load. Sounds good! But what I do not see is how to pass these nice options to make through CMake and QtCreator! One attempt was to specify CMAKE_CXX_FLAGS=-j4 or the like because some comment "in the internet" seemed to suggest this. However, like I already feared: this passes the option to the compiler call - and that is the wrong address for it, so I get an error message. Basically I think that it is 99% a CMake question and maximum 1% a QtCreator problem, so I am asking this question here. And now I am stuck - if not some friendly and knowing person can help me out of this! Thanks for any helpful hint! Cornelis


-- 
Regards,
Konstantin