GPU render slow in 2.77

Hi guys,

I noticed that renders made using Cycles GPU in Blender 2.77 are slower than version 2.76b. Anybody have noticed that too?


While I cant speak to your specific issues, I have noticed SIGNIFICANT slow down in render times under 2.77

5k images that had render times of 4 hours are now taking 60 hours
Flick them back to 2.76b and i get 4 hours again

I also get memory fails (cuMemAlloc error) when the renderer finishes one square and moves onto another.
Renders that use a total of 12gig (over 3GPUs) in 2.76b and render fine are having memory errors when only using 7gig

So for me… 2.77 is slow, unstable and unable to render scenes half as complex as 2.76

Not sure if this helps you in any way.

P.S. this is on a workstation with 12 cores using 3x 980Ti cards for rendering

Thank you, sanjiro666, for your reply. I´ve already send a bug report (, and I waiting for answers. I think developers are working on it. Thanks for your details.

I only have BMW benchmarks for 2.75a and 2.77 - but GPU rendering is definitely slower on the GTX 980Ti. I have also found 2.77 is far more sensitive to tile size.

For example, under 2.75a, the optimum tile size was 960x540 - but with 2.77 that tile size takes more than twice as long and is almost as slow as rendering with CPU.

The optimum tile size in 2.77 I have found is 160x120 - but even this is still 20 seconds slower than the fastest render time I got using 2.75a.

There Sergey close the report and give an explanation. I’m not sure I understood why the issue happens.

Well, I´ve made another test using a file created in version 2.76a. This time, I´ve got better results:

i7 4790
GTX 960
Windows 10 64bits

2.76b - GPU 256x256 - 1:06.58
2.76b - CPU 32x32 - 1:23.50

2.77 - GPU 256x256 - 1:04.77
2.77 - CPU 32x32 - 1:21.69

2.77a - GPU 256x256 - 1:04.42
2.77a - CPU 32x32 - 1:21.84

On my bottom feeding GT 530 the render times are about the same. And, seem a little quicker then 2.76 in scenes where there was some baking. (2.77a)

In another thread someone had their IT guy tweak their graphics card and according to them it is now blazing fast using Cycles. If I had a higher end card I would certainly be pursuing that thinking. Although how many of us have a IT guy at work. Now I have to assume any changes he made you could but that wouldn’t have to be the case I suppose. Since they said he was at it for about three hours. Maybe a tech type might weigh in here.

Sad to say but for now, you should stick with 2.76b
What ever was done to cycles for 2.77 has made it unusable for any serious work.

The developer thread on this subject has gone quiet for some time now.

As much as I love cycles and blender we will be moving back to houdini
Lack of development would be disappointing but great leaps backwards are unacceptable

from top of my head
… it is because of some “experimental” tech was moved to “supported” in GPU rendering (iirc - SSS…), rendering on GPU using simple shaders is still on pair with 2.76b, except for GTX 980Ti which has different problems

@sanjiro666, What GPU do you have?
Why leandrooliveira was having this problem is explained in the report that he had done.
And if you have a GTX 980 Ti or Titan X, there are currently problems with Windows 10. These problems do not occur in Linux or previous versions of Windows.

We run many render machines
Using 780, 780ti, titan x, titan z, 980 and 980ti

While the 980s and 980tis have never performed as we had hoped other than the increased memory (which is essential)
The move to 2.77 saw ALL of our render boxes slower and in the case of the 980 range they became unusable

2-5x slower than the 780s and running into memory issues on even the simplest of scenes.

Cycles in its current 2.77 form is not a viable render for professional work

have you tried compiling your own cycles before? we disable volumetrics, hair, sss and cmj… not only does it reduce the overall kernel size but also renders faster.

Our rendertimes (on many 580s and 590s… so a bit older) with the current version (about 2 week old buildbot) is approx the same as 2.76

To be honest I never even considered this option (artitst not programmer)
I will look into it.

I work with MAX C4D Softimage Modo Lightwave Houdini and Blender
out of all of them Blender is my first choice for fast jobs that will have a short shelf life
We even use if for allot of our 2D animation
Only Houdini stands above blender for me, so we invested allot in hardware for cycles rendering

I will get one of my code monkeys to look into that solution

file is located under blender-git/intern/cycles/kernel/kernel_types.h

You only need to compile once, and then you can reuse that compiled kernel (located under blender\2.77\scripts\addons\cycles\lib)

We only compile sm_20 and are able to reuse the kernel between OS’s fine (compile on linux, copy the file and works fine under windows)

Just shoot me a message directly if you are having any troubles with it all and im not responding in the thread.