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

Bill Hoffman bill.hoffman at kitware.com
Tue Dec 11 08:14:20 EST 2007


Christian Ehrlicher wrote:

>>>
>>>> *         We're using an NMake build tree, is NMake particularly
>>>> slow?  Do any of the other makes work more efficiently?
>>> Be aware that nmake builds are much slower than using devenv, as nmake
>>> starts a cl.exe process for every single file,
>>> whereas devenv calls cl.exe with several source files. This costs, due
>>> to the high process overhead on Windows.
>> I understand that.
> It's not a nmake problem but a problem of cmake. cmake does not support batched build - already opened a bug long time ago because of this.
> 
> 

I am not sure how much faster a batch build would be.  The real issue is 
the dual or more core machines.  Even with a batch build and cl, it 
still only uses one processor, where devenv uses more.  I use gmake and 
cl to get around this with -j N.  However, gmake is slower than nmake 
because it uses the POSIX stat which is VERY slow on Windows.  Someday I 
am going to hack gmake to use the Windows native calls to stat files. I 
almost think that would be time better spent than adding batch cl calls 
to CMake. I would like to see some bench marks on cl batch builds.  It 
will not be trivial to implement and I don't think it would be worth the 
effort unless it has a big gain.

-Bill


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