Cycles is suddenly slower using GPU than CPU

Anyone else encountering this? I mentioned it in the Brecht’s Easter Egg thread but it must not have been considered on-topic as my comments were ignored. I’ve just replaced my 4gig RAM with 16 gig on my Mint 13 desktop, and was trying it out with Blender and Cycles (52402 build)… looking at one of the trees (Arbaro-based Aspen with 81429 faces), it appears the CPU renders the tree faster in the viewport than the GPU does:

CPU… 7.25 (seconds) for 5 frames
GPU… 1:54.32 (minute:seconds) for 5 frames

Transparent is on in Film
Tile size 256 x 256, start resolution 64

I do have a Glossy BSDF node in the leaf shader

Anyone else experiencing this?

Wonder if I need to upgrade to the latest CUDA toolkit for Linux or something…

Bizarre…it just happened after you changed out the ram?

Does it do the same with other Blender builds?

Could we have the .blend to see if we get similar results?

Thanks for your reply, megacal.

Yes indeed, it does. I have a PPA from Irie Shinsuke (currently at 52355) which does exactly the same thing. I’m wondering if the whole “upgraded RAM, noticed GPU slowdown” might be coincidental, though. Right about then was when we went to the newer versions of OiiO and Boost - as updated for those who compile their own in Linux - with that script.

When I went through my initial trials with all this, it was suggested I use the CUDAToolkit 4.2. I’m wondering if that still holds true, now.

I’m copying the file (a tar of the file and texture) to my server: here’s the link.

It was a BlendSwap thing by David Nyul (HUN) of a lake scene I’m trying to convert to Cycles. This always viewport rendered very quickly in Cycles (GPU), as well as the regular Cycles GPU render [F12].

You got me thinking, Megacal… loaded up another scene which, after a few adjustments, rendered just fine, both in viewport and [F12]. So, it’s two scenes, one with a lot of transparency and glossy (a tree) and one with … well, that scene of the lake. Now, to have a look at what is different, what Cycles and the GPU might be choking on… because they did render quickly before.

I kind-of think - call me crazy, but anyway - that there should be a thread for those of us who aren’t totally oh-fay with all the development aspects of Cycles… I’m just talking users who struggle to get basic concepts down.

Like me.

I’ll be the first to admit that whilst I’ve been religiously following that Brecht Easter Egg thread, heaps and heaps of that discussion is way over my head. I’ll continue following it, of course, but it would be nice to be able to post things like the above in a less eclectic environment.

Whadaya reckon? Idea?