[Bf-committers] OpenMP issues with msvc2013 builds

[Sergey Sharybin]

Hi,

We've spent quite a while trying to solve the upcoming stream of reports
about high CPU usage with builds made with msvs2013 in certain situations.
Root of the issue goes to the change made to OMP inplementation back to
msvc2010 days -- they've forced threads to spin for a while after they did
a work. This is a know issue in the library and nobody actually gonna to
fix it [1].

There's one woekaround to solve the issue which is to set OMP_WAIT_POLICY
environment variable to PASSIVE. Unfortunately, since openmp is a dynamic
library and can't be linked statically at all we can't modify environment
variables from within blender using putenv(), this is to be done
externally, before blender.exe starts.

Here's the list of possible solutions:

- Declare msvc full of crap, switch to intel compilers

- Try to hack into vcomp120.dll, trying to figure out the variable, linking
to it and modifying if (so called brain surgery from the blender side). No
idea if it's doable.

- Ask users to set this variable in their environment (Control Panel ->
System -> Environment Variables). For this we can create a .bat script.

- Same as mentioned above, make it a step of the blender installation
process Or make it so blender.exe modivies the registry. Personally i don't
really like this approach.

- Create a small .exe which we put next to blender.exe and will call it
blender-launcher.exe or so. This application will modify the environment
variable and start blender.exe. We could also make it called blender.exe
and rename real blender.exe to blender.bin.exe so all the links and so
continues to work. Here's a quick code of this application [2], would need
to create an icon for it and so but that's details.

Thoughts?

[1] https://support.microsoft.com/kb/2689322
[2] http://www.pasteall.org/53290/cpp

-- 
With best regards, Sergey Sharybin