For Android, when calling ndk-build.cmd you should pass in j# for jobs.
For Android, my command is:
NDK_ROOTbuild.cmd j32C .
For Win32 (Visual Studio) you should turn on /MP and turn off /GM
By turning on multiple processors and turning off the inter-file minimal rebuilding stuff, I got a 10X improvement on build speed.
It was closer to 15X for Android — I have a 32 core machine with 4 physicals, so paralleling helps a lot but I bet everyone on here has more then one core.
For the both settings, it is very easy to put in settings that will take up 100 of your CPU.
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Visual Studio by default turns on /GM but in reality, /GM does almost nothing.
The benefit of using all your cores vs. only compiling a of the lines in C++ file is no contest — on a multicore machine, /MP wins every single time. I haven’t used a single core build machine in a decade or more.
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And as our esteemed forum member dot squid points out, there is less time for tea (or coffee, in my case.)