Do you have Symantec Endpoint Protection or similar antivirus? We found that under certain paranoid settings, even  "ghc --version"  took upwards of seven seconds, and compilation was slowed by a couple of orders of magnitude. We think the AV was scanning the (large) compiler binary, plus any DLLs it loads, plus the source, interface, and object files read and generated, On every invocation. Linking was absolutely dog slow.  We also think the AV was deliberately throttled to never use more than 10% of CPU time, to avoid being noticeable to the user.

It is possible that there are AV settings you can tweak to avoid the paranoia, and trust the compiler, and any other file that has already been scanned once.

 Regards,
    Malcolm (iPhone)

On 17 Sep 2016, at 07:04, Nicu Ionita <nicu.ionita@acons.at> wrote:

No virtualisation, it is a dual boot maschine.
1 CPU would be good :-) In my case it is a very small fraction of it.
Nicu

------ Originalnachricht ------
Von: "A.M." <agentm@themactionfaction.com>
An: haskell-cafe@haskell.org
Gesendet: 17.09.2016 03:20:38
Betreff: Re: [Haskell-cafe] Very _very_ slow compiles on Windows 10

On 09/16/2016 06:10 PM, Nicu Ionita wrote:
 Is anybody else experiencing really slow compilations with GHC 7.10.2 on
 Windows 10?
 
 I use stack to compile the project and run it under a mingw64
 environment provided by Github bash. The CPU usage is very low all the
 time (meaning: GHC does barely use the CPU). On same computer with
 Ubuntu 16.04 it just compiles normally, but under Windows it is for sure
 10x slower, maybe even more.
 
Are you using virtualization? I see the same thing under virtualbox on
Ubuntu. Specifically, even after allocating 12 real CPUs to the VM, I
never see stack-invoked ghc use more than one CPU. On rare occasions,
the linker phase hangs. I have confirmed that ghc reports 12 capabilities.
 
I'm just glad that Windows is not my primary development platform; it's
entirely possible that virtualization is the cause. VirtualBox is not
known for being a speed demon, but the compilation speed is indeed
embarrassing.
 
Cheers,
M
 
 
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