use specify gpu index

[hyebinyoo]

I'm running the following code:
python scripts/run.py --scene data/nerf/pavillon2 --mode nerf --screenshot_transforms /data/hyebin/pavillon2/transforms_test.json --screenshot_dir /data/hyebin/instant-ngp

But it seems like all GPUs are used automatically. The GPUs I currently have are numbers 0 to 9, and I only want to use number 6, but there doesn't seem to be a setting code in the run file.

Where should I change the testbed.cu code to use only a specific GPU index?
I tried changing several places, but it didn't work properly.

Also, is there a part to adjust the number of samples per ray?