[CMake] Compilation speed with CMake/NMake combination, making it faster?

[Jesper Eskilson]

Eric Noulard wrote:
> 2007/12/11, Jason Stewart <jstewart at pobox.com>:
>> This is not scientific but I wrote a quick perl script to compile a
>> simple library that we use (GCTPc). It consists of 70 C files with most
>> of the files between 5K and 6K, a few are as large as 70K. The script
>> just uses the time() function to grab the elapsed seconds and runs three
>> tests. The first runs one cl.exe process with all 70 files with the '-c'
>> flag to only compile. The second compiles each C file with it's own
>> invocation of cl.exe. The last repeats the first, but with the new,
>> experimental, '/MP' flag that does multiprocessor builds.
>>
>> I get the following times for these files:
>>     all files      : 2 seconds
>>     single files : 7 seconds
>>     mp build   : 1 second
>>
>> I repeated this test with a set of 15 C++ files that are larger with
>> template code and that take significantly longer and I got the following
>> times:
>>     all files      : 60 seconds
>>     single files : 78 seconds
>>     mp build   : 51 seconds
>>
>> So, even on the single processor build the single invocation is almost
>> 25% faster.
>>
>>
>> Take it all with a grain of salt.
> 
> I'm not a big MS Platform user but I like the idea
> of compilation speed-up very much.
> 
> I personnally use ccache (http://ccache.samba.org/)
> on Linux + gcc and there is x2 up to x4 _SPEEDUP_
> (when recompiling since initial compilation is slower)
> on a C++ project with 50+ files with moderate template usage.

Yes, recompiling goes faster, but if you actually have made any changes 
to the source code (which is often the case when you're compiling ;-)) 
then ccache won't give you anything.

Most people I've seen claim that ccache is useful are people who are 
stuck with a build system with broken dependencies who need to do "make 
clean" a lot. ;-)

Actually, ccache comes in its best light when you can use it for sharing 
build-results.

--
/Jesper