Multi-context shared resource performance with VAOs

Operating System: Windows 10 64-Bit

Mesa Version:  13.0.1 (though the same behavior is seen with the latest version)

Renderer: llvmpipe


I have an application with multiple OpenGL windows (which optionally uses mesa) which I am currently transitioning from a shared render context to multiple render contexts with list sharing. Due to this change, VAOs can no longer be shared between windows. I'm finding that when using a VAO (e.g. through DrawElements) built from shared resources (not only in that case, but even in that case) that there is a significant performance penalty the first time. Looking at the profile, it appears to be getting into the llvm pieces. I'm finding this a bit surprising since my view of a VAO was that is was more lightweight and thus didn't expect much overhead in creating a new VAO from existing resources (To be explicit, the penalty is not on VAO creation but on first time use). So some questions:


  1.  Any insight into why this is occurring?
  2.  Any way to mitigate the symptoms?
  3.  Any possibility of fixing it in a future release?


I'd appreciate any thoughts you can provide.


Thanks,

Rob Conde

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