I have a Intel® Core™ i5-2500 CPU @ 3.30GHz × 4 system with 8gb ram (64 bits) and a Nvidia GeForce GTX 560 Ti/PCIe/SSE2 graphics card.
I have a dual boot with Ubuntu 12.04 and Windows 7. I am an avid Ubuntu fan and defender of the OS, but last week I installed the new Blender release 2.63a under Win 7, then I did a benchmark test of a heavy glass logo rendered in cycles. Settings for Windows use the CUDA from Nvidia...but...under Ubuntu Blender there isn't a setting for CUDA (although it does see the Nvidia card). I rendered the same file under both OSś and to my surprise Windows rendered twice as fast as Ubuntu, and the update of the display shader window was also much faster under Windows.
I've been following this online and everyone says Ubuntu should be faster...WHAT THE HECK?
From the sound of it, you are comparing GPU vs CPU rendering.
I suspect the issue is not the OS, but the video driver. Are you using the nVidia binary driver or whatever came with Ubuntu?
I did try " additional drivers " in the preferences menu, but the rendering is even slower! Is there another driver I'm not aware of?
Was there a change from previous Blender versions?
Only the upgrades via the PPA