Sss gpu render speed degradation #55351

New Issue

Yegor · 2018-06-06T15:25:12+02:00

Yegor commented

2018-06-06 15:25:12 +02:00

System Information
CentOS, Nvidia GTX 1070

Blender Version
Broken: 2.79 713027b832 daily build, 2.8
Worked: 2.79b official

Short description of error
Rendering sss on gpu take more time in the daily build and 2.8.
This particular scene: 2.79b - 1:12, 2.79 daily build - 1:23
With more complex shading it was even 1:12 vs 1:38, and 1:42 on 2.8
Rendering on CPU is the opposite - faster in the daily build.
The settings are important. This behavior is only for:
branched path tracing
subsurface samples = 3
hdri as a light source (multiple importance is on)

And what's more, if you set the subsurface in the shader to 0, you'll get almost the same render time, but in 2.79b it'll have noticeably less noise.
Don't know if it's relevant and should i create a new report on this.

Exact steps for others to reproduce the error
Open the scene.
Hit render.
Repeat in the different versions of blender.
blender_cycles_gpu_speed_degradation.blend

**System Information** CentOS, Nvidia GTX 1070 **Blender Version** Broken: 2.79 713027b8325 daily build, 2.8 Worked: 2.79b official **Short description of error** Rendering sss on gpu take more time in the daily build and 2.8. This particular scene: 2.79b - 1:12, 2.79 daily build - 1:23 With more complex shading it was even 1:12 vs 1:38, and 1:42 on 2.8 Rendering on CPU is the opposite - faster in the daily build. The settings are important. This behavior is only for: branched path tracing subsurface samples = 3 hdri as a light source (multiple importance is on) And what's more, if you set the subsurface in the shader to 0, you'll get almost the same render time, but in 2.79b it'll have noticeably less noise. Don't know if it's relevant and should i create a new report on this. ![2.79b.png](https://archive.blender.org/developer/F3602059/2.79b.png) ![2.79_daily.png](https://archive.blender.org/developer/F3602058/2.79_daily.png) **Exact steps for others to reproduce the error** Open the scene. Hit render. Repeat in the different versions of blender. [blender_cycles_gpu_speed_degradation.blend](https://archive.blender.org/developer/F3601962/blender_cycles_gpu_speed_degradation.blend)

Yegor commented

2018-06-06 15:25:12 +02:00

Added subscriber: @YegorSmirnov

Steffen Dünner commented

2018-06-06 16:35:12 +02:00

Added subscriber: @SteffenD

Steffen Dünner commented

2018-06-06 16:35:12 +02:00

First question: Are you using "Hybrid" rendering in master?

I mean this (not available in 2.79b):

I tried with and without CPU enabled (I have a whimpy 10years old XEONx2 with a GTX780 3GB so the CPU is the weakest part) and here are my results:

Version	Tile Size	CPU enabled	Render Time
2.79b	256x256	No	1.43min
Master	256x256	Yes	12.34min (!!!)
Master	256x256	No	1.45min
Master	32x32	No	1.29min
Master	32x32	Yes	1.31min (CPU is still taking too long per tile)
Master	16x16	Yes	1.22min (Now the tiles are small enough for the CPU to no longer slow down the whole process)

As you can see tile size is king and very important. There was a change after 2.79b where small GPU tiles were no longer a problem so it could be used together with usually smaller CPU tiles.
Most likely your "regression" is none but your render settings just need a little adjustment of the tile size to render even faster than 2.79b.
If you have a halfway decent CPU you will render a lot faster even.

First question: Are you using "Hybrid" rendering in master? I mean this (not available in 2.79b): ![Screenshot at 2018-06-06 16-20-05.png](https://archive.blender.org/developer/F3602475/Screenshot_at_2018-06-06_16-20-05.png) I tried with and without CPU enabled (I have a whimpy 10years old XEONx2 with a GTX780 3GB so the CPU is the weakest part) and here are my results: | Version | Tile Size | CPU enabled | Render Time | -- | -- | -- | -- | | 2.79b | 256x256 | No | 1.43min |Master|256x256| Yes| 12.34min (!!!) |Master|256x256|No| 1.45min |Master| 32x32| No|1.29min |Master| 32x32| Yes|1.31min (CPU is still taking too long per tile) |Master| 16x16|Yes|1.22min (Now the tiles are small enough for the CPU to no longer slow down the whole process) As you can see tile size is king and very important. There was a change after 2.79b where small GPU tiles were no longer a problem so it could be used together with usually smaller CPU tiles. Most likely your "regression" is none but your render settings just need a little adjustment of the tile size to render even faster than 2.79b. If you have a halfway decent CPU you will render a lot faster even.

Yegor commented

2018-06-06 17:00:34 +02:00

No, i used GPU only render with 256x256 tile size.
And by the way, i didn't know about smaller tiles improvement! Now i've tried 32x32 and got 1:18. But it takes still a bit more than 256x256 on 2.79b (1:12)

No, i used GPU only render with 256x256 tile size. And by the way, i didn't know about smaller tiles improvement! Now i've tried 32x32 and got 1:18. But it takes still a bit more than 256x256 on 2.79b (1:12)

Steffen Dünner commented

2018-06-06 17:04:50 +02:00

Depending on your hardware and the scene configuration you might need to fiddle a bit with the tile size to find the sweet spot.
In my case it's almost always 32x32 or 64x64 but that can vary. Like with your scene it's 16x16 although I didn't test 8x8.

Depending on your hardware and the scene configuration you might need to fiddle a bit with the tile size to find the sweet spot. In my case it's almost always 32x32 or 64x64 but that can vary. Like with your scene it's 16x16 although I didn't test 8x8.

Yegor commented

2018-06-06 17:09:56 +02:00

No no, the tile size is understood and i'm really happy with those news. On my hardware it works best on 32x32, but the thing is even with this sweet spot it's still a bit slower than 2.79b with 256x256 GPU only. I could get the exact same time with the hybrid render - 1:12, but it's still more, than gpu alone on 2.79b, right?

Yegor commented

2018-06-06 18:14:43 +02:00

Tested some more scenes and i guess it's scene related and can vary a bit. The speed is about the same. Somehow the tile size speedup slipped away from me. The light behaves a little different, though, but the task can be closed now, i think.

Philipp Oeser commented

2018-06-07 09:19:48 +02:00

Added subscribers: @Sergey, @brecht, @lichtwerk

Philipp Oeser commented

2018-06-07 09:19:48 +02:00

Changed status from 'Open' to: 'Archived'

Philipp Oeser closed this issue

2018-06-07 09:19:48 +02:00

Philipp Oeser self-assigned this 2018-06-07 09:19:48 +02:00

Philipp Oeser commented

2018-06-07 09:19:48 +02:00

Generally this might still be of interest to @Sergey and @brecht, but since this is somewhat tamed by the tilesize speedup, will archive as @YegorSmirnov suggested....

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Sss gpu render speed degradation #55351