Unless a hardcore Windows systems hacker comes along, you’re not going to get more than partisan comments (which I won’t do) and speculation (which is what I’m going to try).
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File system – You should try the same operations (including the
dir) on the same filesystem. I came across this which benchmarks a few filesystems for various parameters. -
Caching. I once tried to run a compilation on Linux on a RAM disk and found that it was slower than running it on disk thanks to the way the kernel takes care of caching. This is a solid selling point for Linux and might be the reason why the performance is so different.
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Bad dependency specifications on Windows. Maybe the chromium dependency specifications for Windows are not as correct as for Linux. This might result in unnecessary compilations when you make a small change. You might be able to validate this using the same compiler toolchain on Windows.