[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 20:00:27 CEST 2013

On 23/06/2013 18:03, Brecht Van Lommel wrote:
> 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?
Apologies, not Toolkit 5.0 related, after performing your tests below 
discovered it goes back further.

> * What is the version number of the build before the toolkit change
> that still gave good performance (to narrow down the revisions)?
*blender-2.67-r57293-win64* is okay, Viewport performance same before 
and after F12 Cycles render.

*blender-2.67-r57348-mingw64* Is okay except for border render issue, 
otherwise same as above.

*blender-2.67-r57476-win64* First versions (I have) that shows the 
issue, Viewport performance same as previous version until F12 Cycles 
render, then very slow jerky Viewport performance.

> * Does this really only happen with GPU rendering, CPU rendering does
> not show the same issue?
Interesting test idea. Same issue after either GPU or CPU F12 Cycles render

> * What is performance like with VBO's switched off before rendering
> (in case the rendering somehow switches them off)?
Not as smooth, around 10-15fps but still faster than after rendering, 
which then feels around 2fps.

> * What is the performance like with the NVidia card, is it also 2fps
> or somewhere in between?
Not yet tested, once wiring configurations are changed will email 
results. Thought quick reply with above answers would be appreciated.

> * Is a Blender restart needed or does reopening the scene solve the issue too?

Interesting, reopening the same scene without restarting Blender also 
solves the issue, until an F12 Cycles render is performed.


> 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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>> Bf-cycles at blender.org
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