[Bf-committers] OpenMP issues with msvc2013 builds

[Martijn Berger]

On Wed, Aug 6, 2014 at 5:55 PM, Campbell Barton <ideasman42 at gmail.com>
wrote:

> Theres been some issues with OpenMP, but am wary of kicking out entire
> technology just because we can't set an environment variable? (ok, of
> course theres more to it - but seems a weak reasoning still).
>

I would not want that to be the reason. And it is not easily kicked out
anyway. MS should fix this and until then we should just add a launcher in
my opinion.

You are right these are 2 separate issues.

But in my mind there does exist an issue that with multiple technologies to
create threads you can easily create situations that are non optimal and
even decremental to performance.
We have a lot of places where we use a lot of threading / parallelising
systems in a lot of different ways. This is partly due to 3rd party libs
all doing their own thing.
But the other part is us just adding a bit of OpenMP there building a task
scheduler into that, adding some static threads there etc etc etc.
The argument I made is not specifically targeted at OpenMP. But rather at
the whole zoo of solutions we have everywhere and the fact that we seem
open to adding yet more.
Any threading is hard but reading and maintaining code that does it in a
100 different ways that all might interplay in weird and undefined ways
depending on platform and implementation is even harder.
CPU's do not seem to be getting faster but rather more parallel and we need
at least consider trying to find a good way how to handle that. To me when
we would make the whole of blender more task oriented that would amplify
this potentially. Besides I love thinking about these kinds of issues and
the technical discussion they result in.