Redshift: Multiple GPUs or one GPU per render thread?

[RR, Schoenberger]

Dear RR Knights.

 

Some information about the question if you should assign one frame to a single GPU or to all GPUs.

 

As you might know, we have implemented the Redshift Benchmark as a Scripted Job (rrSubmitter menu) in 8.2.08.

The benchmark result table shows the render time using all GPUs, the first two GPUs 0+1 and each of the GPUs 0,1 separated.

 

And we have received some results for Windows from some render farm sites.

This is an example of a 8GPU machine:

1GPU:    1006s

2GPUs:    522s   (*2= 1044s       +3% time compared to 1 GPU per frame)

8GPUs:    151s   (*8= 1208s     +20% time compared to 1 GPU per frame)

 

By using 2 GPUs for one frame, the render time could increase by 3% in total.

Using 8 GPUs for one frame, the render time was increased by 20%.

 

Notes:

• During our tests, we had a time difference of + 40seconds per frame for the same GPU on the same machine.
  We will investigate and try to eliminate this issue if possible.
  It could easily affect the test result by a few %.
• The 8GPU test was only 151 seconds, a good benchmark should run at least 5 minutes.
  It could easily affect the test result by a few % as well.
  The only solution would be a test scene that takes more time to render.
  (For the redshift artists: Which render setting should be increased to double the render time easily? )
  
  

 

PS:
Comparisons between using the same GPU and machine on Windows and Linux is next on our list in case you are interested.

 

 

regards,
Holger Schönberger

 

Please use the rrKnights Tavern
or our support system for new questions.

[Morten Bartholdy]

Hi Holger,

I just saw this, trawling through the Tavern to find something else. Very interesting info - thanks.

If you quickly want to double rendertime, I guess the fastest way is to increase Unified Samples min samples, so if you are having min 8 max 256, setting min to 128 might do the trick. It will likely require some experimenting, as it is adaptive and there is no certain way to exactly double rendertime.

Cheers

Morten

[H.Schoenberger]

Thanks for the hint, I might double the resolution next time.
It does not have to be exact 2 times the render time, it just needs to be compareable between all machines.