[CMake] VS2012 builds using v3.1.0 are a lot slower than v2.8.12

[Yves Frederix]

Ok, so it all seems to boil down to the following:

 - 2.8.12: "cmake --build" uses devenv to build, which in turn picks
up a setting ("maximum number of parallel project builds") from the VS
IDE at build time. As this was set to 8 on my machine, by default the
build used parallellization with 8 cores with a fast parallel build as
a result. I verified that after changing this setting in the IDE to 1,
the build no longer works in parallel, with longer build times as a
result.

 - 3.x: "cmake --build" uses MSBuild, which uses a command line switch
/m to control the same behavior. In absence of this command line
switch, the default behavior is equivalent to /m1 (see
https://msdn.microsoft.com/en-us/library/ms164311.aspx), which means a
non-parallel build and longer build times than for 2.8.12. A way to
test this in practice, is to run a build command with native build
options like  'cmake --build . --config Release -- /m'. I checked and
this indeed works as expected.

The above explains all my initial observations. However, the fix is
not very handy. As I understood, one does not know until build time
what exact build (devenv or msbuild) will be used by CMake, so simply
always adding '-- /m' to the build command will not work (devenv
doesn't like /m). Assuming that changing the default command line
options to MSBuild inside CMake is not a valid solution, I am
wondering if there is currently a way to set additional build options
for MSBuild only from inside the CMakeLists.txt file? Or,
alternatively, is there a way to check which build program will be
used before actually running the build?

Yves


On Tue, Jan 20, 2015 at 10:46 PM, Paul Smith <paul at mad-scientist.net> wrote:
> On Tue, 2015-01-20 at 16:02 -0500, Paul Smith wrote:
>> > I think devenv is used instead of msbuild when the solution has
>> > fortran projects.
>>
>> I certainly don't have any Fortran projects--!!
>
> I think I figured it out: on our build servers we don't delete
> everything and start over from scratch all the time (only for our
> official release builds).
>
> We recently upgraded our cmake from 2.8.12.2 to 3.1.0 and I think that
> the systems where we were seeing this problem had CMakeCache.txt files
> left over from when we were using CMake 2.8.12.2, and those files had
> CMAKE_MAKE_PROGRAM set (we never set it by hand, even back then, but
> maybe the older version of cmake added it to the cache on its own?) to
> devenv.
>
> Certainly when I went in and looked at CMakeCache.txt that value was set
> to "devenv.exe".  If I regenerated the CMakeCache.txt from scratch, it
> was no longer set.
>
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