Hi, blender community.
I have a question. If i had multiple GPU’s would it affect blender viewport rendering performance?
Yes, Blender use all (Nvidia) cards set in User Preferences > Sytem for viewport too.
Cheers, mib
Hi, are you sure about that? because i have read that it uses only one GPU card for viewport rendering. Im confused right now…heh
http://blender.stackexchange.com/questions/5228/how-will-two-gpus-improve-cycles-performance
You need to differentiate between viewport (OpenGL) performance and render performance. Unlike e. g. a computer game, Blender can not utilize multiple cards for geometry display, sculpting etc. in OpenGL mode.
But rendering of any kind (be it rendered viewport or final render) uses all available CUDA devices - if so configured.
That’s what the poster in your link meant when he wrote:
“The more GPUs, the more tiles being rendered simultaneously, so two GPUs will cut rendering time almost to one half. Other than rendering, only one GPU will be used for calculations and to refresh the screen.”
Hi, before I wrote this I run a test with my two GPU and they are work both.
I think the article on stackexchange is about SLI and Cuda applications does not use SLI.
Cheers, mib
I tried this too (the “old” 760 if you remember mib 
), the viewport performance while rendering on the second gpu is much better than rendering on the first, where the monitor is attached (and the opengl rendering should take place). You have to change the card to use for rendering in the user preferences. Still it’s not totaly “lag-free” because there’s always a back-and-forth with BVH and the CPU.
I don’t think you can change where opengl is rendered, it will always be the card where the monitor is attached. It also won’t use multi-gpus for opengl. That may be different if you use SLI, I don’t know.
OT: Strange enough, I’m even able to play a game on GPU1 while GPU2 is rendering (but it’s really laggy), but if I play some flash video in Firefox Blender drops dead immediatly without warning.
Related question:
I have installed a GTX 970 (see signature below). I had originally hoped to use integrated graphics for display and the discrete GPU for rendering only - this was not possible so I ended up disabling the integrated graphics and connecting my monitor to the GPU. Blender runs fine but I am wondering if a very small investment in a second GPU (eg GT 610 or 720) for driving the display only would be a worthwhile investment (ie what kind of improvement to render times could be expected)?
I presume that a GT 610 or 720 would be okay for running Blender even with DDR3 memory (ie no lag); is this the case and are there any foreseeable problems with this approach?
Cheers