[CMake] Performance issues on very large project

[Steven Stallion]

All,

I am currently working on a very large project that contains over 500
(yes, really) listfiles. A co-worker was looking into some performance
issues we were seeing during configuration and found something very
interesting. Currently configuration is taking 1m57s across several
configurations using Mac OS X as a host and the latest .dmg from
cmake.org (3.5.1).

We have a core module that provides a number of helper functions and
macros (completely stateless) that is included by most of this
listfiles (nearly 400 of them). We found that an include guard was
missing, after adding that configuration now clocks in at 1m30s.

Taking things a step further, we removed includes of the module, and
simply included it once in the top-level listfile. Configuration then
dropped to about 55s.

The results above seem to indicate a possible file I/O bottleneck.
This is very surprising to me - these builds are being run on recent
core-i7's with SSDs. Is anyone else on the list dealing with large
projects or similar configuration issues?

TIA,

Steve