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I am using Blender 2.66a a nVidia GT 520 and Ubuntu 13.10. I wanted to enable GPU rendering. But in the System Panel there is no 'CUDA' Option.
I know that this Card supports CUDA, because I have tested it on Windows 7 (dual- boot) too and it worked.
I installed the proprietary GPU driver using

sudo apt-get install nvidia-current

Any ideas why it doesnt work?
Thanks in the preface

Peter Parker
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    Is there any particular reason you are using that version of Blender? – gandalf3 Jan 02 '14 at 22:15
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    Yes, its the latest Version, thats available in the official repository! – Peter Parker Jan 03 '14 at 14:11
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    I have tried it using the latest Version (2.69) and it worked, but GPU rendering takes more time and CPU rendering. Do I need to adjust some settings ? – Peter Parker Jan 03 '14 at 14:22
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    It's really odd that GPU would take longer than CPU. If you're on a laptop, it's entirely possible that Blender is mistakenly using your onboard graphics, rather than your nVidia card. Also keep in mind that you have to select which card to use in the User Preferences, as well as choosing GPU rather than CPU in the Render panel. It'd be nice if these two settings would affect each other, or at least provide a warning, but they didn't the last time I made this mistake. – Matt Jan 03 '14 at 17:52
  • This doc: http://www.blenderguru.com/4-easy-ways-to-speed-up-cycles/ will also help you trouble shoot some things. E.g. tiles with a size that is a power of 2 are MUCH more efficient than tiles of arbitrary size. – Matt Jan 03 '14 at 17:54
  • @Matt Can you prove that? I did some testing here and I saw no evidence of any speedup. – gandalf3 Jan 03 '14 at 20:50
  • Sure thing, I'll post some of my benchmarks when I get a chance. In short, I usually see a 10% decrease in render times if I use tile dimensions that are powers of 2, versus dividing my image into equal portions. Part of the problem is that render time depends on a LOT of other things too. Even the order in which the tiles are rendered can have an impact on render times. I'll try and provide some examples... – Matt Jan 03 '14 at 20:57
  • Ok, in the User Preferences/System I switched the Compute Device to CUDA / nVidia GT 520, also I set Device (in the Renderpanel) to GPU Compute (Supported Feature Set)

    GPU Rendering now takes 6.67 seconds (Tile Size 256:256) and CPU Rendering the same scene takes 1.85 seconds (Tile Size 16:16)

    Is there an other possibility to speed up GPU Rendering, or should I instead use CPU Rendering.

    @Matt Thank you

     – Peter Parker Jan 04 '14 at 09:52
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    @Peter Parker That's really.... REALLY odd. It's easier for me to believe that you have a really strange scene, than to believe CPU is actually faster than GPU, IWC yes, I do believe there's a way to speed it up, I just don't know what it is. I'd love to take a look at the scene you're rendering and see if it fits one of the strange cases I've come across. – Matt Jan 05 '14 at 16:06
  • That's really weird. Is your GPU from the 70's or 80's and your CPU from the future? While this is a duplicate of what Vader posted above, this would be an interesting discussion to continue, or even an interesting question in its own right. – Keavon Mar 04 '14 at 02:21
  • @Matt Sorry I didnt answer... this is the file (http://www.file-upload.net/download-8706409/kugel-auf-karo.blend.html) – Peter Parker Mar 12 '14 at 17:46
  • No worries, I'll try to take a look at it this evening and let you know what I find. – Matt Mar 12 '14 at 18:36
  • Well, I'm afraid I don't have any good answers for you :-/ It's not one of the weird situations. I rendered it 4 times. For CPU with tiles @ 64x64, I got 7:19. For GPU @ 64x64, I got 1:49. Then I changed the tile size. CPU @ 512x512 I got 8:26, and for GPU @ 512x512 I got 1:19. The only thing I can figure is that there's a bottleneck between your GPU and mobo and that using tiles so small is causing it to swap RAM/VRAM back and forth more often than it needs to, and the overhead in swapping that RAM is killing your GPU render time. Try a higher tile size, but IDK what else to try. – Matt Mar 13 '14 at 03:40

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I agree with @Matt, especially if you are on a laptop. Whether you are on a laptop or a desktop PC, I would check the following settings in Blender. Also, when using GPU rendering in Cycles, make sure to check the settings in the Properties tab -> Performance -> Tiles. By default the two numbers under the "Tiles" settings usually are 64 x 64 (pixels). If you are able to get your Nvidia GT 520 video card to work, try bumping up those numbers to 200 x 80 and see if that helps. The other thing i recommend checking is the "Sampling" menu in the Properties panel. If the final render has a high sample number (i.e. - 800 or above), that can also cause render time to be slow. enter image description here

theBrokenVerticie
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CUDA level support is different between GPUs, see this link. Higher CUDA compliance results in better speedup. As I remember, Blender needs at least CUDA 2.0 features, but higher level of CUDA compliance is better.

Earlier Blenders did not even allow using CUDA below 2.0.

It seems that your GPU is CUDA 2.1 compliant, check if your CUDA driver is the latest, too. My guess is that your driver shows a supported version < 2.0 to Blender 2.66a, and so Blender 2.66a did not show CUDA support.

Also, others' comment about optimizations are also very valid.

TFuto
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