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

Brecht Van Lommel brechtvanlommel at pandora.be
Sun Jun 23 19:03:42 CEST 2013

I have no idea how this is possible, all the toolkit changes is code
that runs on the NVidia graphics card, not how it interacts with other
graphics drivers. So perhaps it's another recent change in Cycles or
elsewhere in Blender that is causing this?

* What is the version number of the build before the toolkit change
that still gave good performance (to narrow down the revisions)?
* Does this really only happen with GPU rendering, CPU rendering does
not show the same issue?
* What is performance like with VBO's switched off before rendering
(in case the rendering somehow switches them off)?
* What is the performance like with the NVidia card, is it also 2fps
or somewhere in between?
* Is a Blender restart needed or does reopening the scene solve the issue too?

Can anyone else confirm this problem?

On Sun, Jun 23, 2013 at 5:36 PM, David Black <db4tech at yahoo.co.uk> wrote:
> 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
> restrictions).
> 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.
> David
> --
> 3d-designs-davidblack.blogspot.com
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