I have an unusual problem. I render a frame and it takes 1:46. Seven frames later it takes 2:18 to render a frame. Fifteen frames later it takes 2:34. After a few hours of rendering it takes over 5 minutes to render a frame. I am using Blender 2.79b with an Acer Predator G1-710 Intel i7-7700 3.6 GHz Nvidia GeForce GTX 1080 and Windows 10 64 bit. My animation is about 17,000 frames long and I use hair and particles and transparencies. I have set Cycles render using the GPU. I am rendering single layers. The workaround is for me to close Blender, re-open it and continue rendering where I left off. The render time for the next frame is then 1:56. I do not have this problem rendering the same file on my Mac nor on my old PC. So, does anyone have any ideas as to how I can achieve a relatively consistent render time for each frame?
I am having the same issue, where the rendering of frames takes longer & longer, in my case the render time of the 1st frame is @7:18 min & the 2nd frame takes @8:45 min & it gets progressively worse, after 3 hours a single frame takes 15-17 mins to complete. My rig is a i5 with 32Gig of RAM with a NVDIA GTX 1050 Ti & using SSDDs for temp files & paging. I am also running Blender 2.79b (same issue in 2.79) using Cycles with Device set to CPU (as my GPU only has 4Gig of VRAM & cannot render my blend file). I have managed to reduce the render time from 30ish min per frame (this time appeared to be pretty consistent) by disabling “Hair BVH” under Rendering Performance Panel & baking the Background objects (Walls etc). The slow down appears to be in the “Building BVH” phase of the Rendering Process.
WOW!!!, I believe I may have come upon a resolution to this issue (well in my case anyway), I found by reducing the No of steps under the Particle, Render settings from 9 to 6, My render times are now around 3 min per frame & I am able to use my GPU for rendering my animation. It appears there is not much difference in the quality of the output & I am yet to run a full animation batch job but I am shocked by my test results so far. 