[Bf-cycles] Blender Viewport performance issue after Cycles render (since changing to CUDA Toolkit 5.0)

David Black db4tech at yahoo.co.uk
Sun Jun 23 17:36:45 CEST 2013

Hi Brecht,

Just discovered an interesting issue, seems to have been introduced 
since Blender changed to CUDA Toolkit 5.0. Not related to Cycles render 
speeds, which consequently have received a great boost after code 
re-factoring. Issue is connected with Viewport performance after 
performing a Cycles render.

*Issue outlined below:*

Upon opening a complex scene, with a heavy particle system (particles 
Viewport setting of 1, Child particles 0), Viewport navigation (VOBs 
enabled) with an Intel HD 4000 (part of i7 CPU) is extremely fluid, like 
30fps or more, (much slower on GTX 580 due to double sided Normals 
With recent Blender versions, everything is fine until a F12 Cycles 
render is performed (does not happen with Viewport render), after which 
Viewport navigation becomes extremely sluggish, feels like 2fps. Hiding 
the heavy particle object returns full Viewport performance, once object 
is unhidden Viewport is back to a crawl. Closing and opening Blender 
with the same scene and everything is back to normal, until the next F12 
render is performed.

Blender versions prior to Toolkit 5.0 changes, Viewport performance 
remains just as fluid after a F12 Cycles render, also tested Blender 2.67b.

Today's BuildBot version (official) blender-2.67-r57660-win64 produces 
the sluggish Viewport issue after a F12 Cycles render.



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