[CMake] Tips on reducing configure time

[Eric Noulard]

Hi Victor,

Le mer. 14 nov. 2018 à 10:20, Poughon Victor <Victor.Poughon at cnes.fr> a
écrit :

> Hi all
>
> I am working on a large C++ project using CMake (
> https://www.orfeo-toolbox.org/) and our 'configure' step takes quite a
> lot of time. This can be annoying for developers working on features where
> the configure step needs to be re-run, or for CI in general.
>

Could you give us a clue on "takes quite a lot of time"?
Are we speaking of tens of seconds, minutes etc... ?


>
> We have looked into it a bit and it seems like one issue is that the
> configure/generate steps do a lot of small files I/O. Specifically, using:
>
>     inotofy-wait -mr <build_dir>
>
> shows that "cmake ." causes about 150K file access/modify, etc. There are
> some especially guilty looking files like 'Makefile2.tmp' or 'progress.tmp'
> that appear thousands of times in most of the log file.
>
> I have an SSD which somewhat helps, but for colleagues still on mechanical
> drives this is especially painful. Is there a way to disable writing all
> those files to the disk?
>
> Any other tips on optimizing the performance of 'cmake .'?
>

Did you try to test drive a switch to ninja generator ?
Ninja generator generates only two files (build.ninja and rules.ninja) you
won't have the "mny small files issue".
You can have long configuration times as well but not coming from file
access.




>
> Thanks,
>
> Victor Poughon
>
>
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-- 
Eric
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