Servo build time on Windows 10 is far too slow

[jasonwilliams]

Building Servo on Windows 10 is taking over an hour for me quite regularly.
I've tried various fixes, such as turning windows defender off for that directory but that hasn't made much of a difference.
I understand both machines are different and the difference will vary on OS's but i'm talking orders of magnitude in differences here.. If anything, my windows machine should be faster as its using a modern cpu with a lot more cores.

Specs
Windows 10:
Ryzen 7 1700 @ 3Ghz 8 Cores 16 Threads
16GB DDR4 Ram
Cmder ConEmu (sometimes powershell, no difference)

Mac Sierra 10.12.6:
My Mac is 2.5 GHz Intel Core i7 4 Cores 8 Threads
16GB DDR3

Fresh Build
Here is Servo being updated & built after only 1 day of being stale (did a git pull and built the day before)
https://gist.github.com/Jayflux/b535be2b51ebb4b61a3f4a53a6a5dabd
1 hour and 15 minutes.

Here's the MacOS fresh install (target folder deleted before hand)
https://gist.github.com/Jayflux/b0013c94f116780a7ee64f2dffd6299d
only 30 minutes.

Not only is the MacOS install 45 minutes faster, its also a fresh install, it should be slower if anything.

Changing a line of code then rebuilding
Changing a single line of code in servo/lib.rs then doing a rebuild:
https://gist.github.com/Jayflux/f4bcb9d4d0647d906098637ea2c3e1c6
Only 1:46 on my Mac

on Windows this is over 10 minutes (sometimes 15 minutes).
[Sorry i don't have a gist at this time i will update later]

Summary
Something is very wrong here, trying to dev on Windows 10 is just not possible with these build times. Is anyone doing any investigation into this?

[SimonSapin]

I recently built Servo in 28 minutes (with dependencies already downloaded but with a clean target directory) on Windows 10 with Intel i7-6920HQ. In addition to (the parent of) the git repository, I have C:\Users\Simon\.cargo and C:\Users\Simon\.rustup excluded from Windows Defender.

[jasonwilliams]

@SimonSapin thanks, i will add those 2 to the exclusions.
How are you developing on Servo at the moment? Are you using the Visual Studio Debugger? or adding lines of code and rebuilding?
If the later how long are rebuilds taking you

[jasonwilliams]

Here is a fresh build with my .cargo and .rustup folders excluded from Windows Defender
https://gist.github.com/Jayflux/9d27cc98f2cc4d7501ab3d019d99d70e
52 mins

It spends a long time in link.exe

[SimonSapin]

Sorry, I don’t have more than that one data point. Windows is not my primary environment, I only installed it recently for some WebRender stuff.

[jasonwilliams]

Sounds like this is related rust-lang/rust#37543