[CMake] Parallel build setup question

Sat Feb 17 02:06:53 EST 2018

Thanks also for this hint: I will give it a try!

Regards, Cornelis

Am Freitag, den 16.02.2018, 21:35 +0300 schrieb 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.q
t.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
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