Add support for Half dtype and mixed precision training.

[maskjp]

Hi,

Thank you for this great library and torch-points3d.

I made some modifications to support mixed-precision training.

The major changes are as follows:

• template kernel function in interpolate_gpu.cu sampling_gpu.cu and ball_query_gpu.cu.
• Change AT_DISPATCH_FLOATING_TYPES to AT_DISPATCH_FLOATING_TYPES_AND_HALF;
• Change atomicAdd to gpuAtomicAdd (in pytorch THCAtomics.cuh);
• Add custom_fwd and custom_bwd in torch.autograd.Function to allow autocast;
• fixed bug of sampling_gpu which the first element of idx output is always 0; (But I found that the output of GPU version and CPU version are not the same. I haven't fixed this.)

The modified version passed the tests in the test folder. I didn't see affection on full-precision training. And I tried to train the PointNet2 model in the torch-point3d library in a mixed-precision style, it works.

[nicolas-chaulet]

Amazing!!! Thank you so much for contributing, this is a really needed feature. Tagging @CCInc so that he can take a look as well.

[clee-ai]

@maskjp Thanks for the contribution!

I'm curious which version of pytorch you compiled against, did they change the tensor namespace to torch at somepoint?

I'm guessing the models use ~50% the memory compared to full precision? Did you notice any training speed increase too?

[clee-ai]

@nicolas-chaulet we should add precommit.ci to this repo, so we can ensure consistent formatting on PRs, what do you think? Also, maybe we could add a pytorch version matrix to unittesting? Maybe 1.7.0 to latest?

[maskjp]

I'm guessing the models use ~50% of the memory compared to full precision? Did you notice any training speed increase too?

Hi,@CCInc,

I used torch1.8.1+cu111 to compile it. About the tensor namespace, torch tensor has a higher level, we can also use at too. I just noticed that in chamfer_dist.cpp, cubic_feature_sampling.cpp the torch namespace are used but interpolate.cpp, sampling.cpp and ball_query.cpp used at tensor. I refer to the toturial of pytorch and torch_geomtrics and decide to use torch tensor.

Yes, the modification saves the memory, but I didn't see the training speed increase too. The speed also depends on the model architecture, ops, and io.

[nicolas-chaulet]

Looks good to me, @CCInc could you please verify that the gpu tests pass on your machine? I don't have access to gpus anymore... Thanks! And yes to pre-commit ci!

[clee-ai]

@maskjp I'm getting an issue with the testing, it seems like the cpu and gpu fps are not matching up?

FAIL: test_gpu (test.test_fps.TestFps)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/mnt/f/data/PC/torch-points-kernels/test/__init__.py", line 7, in wrapped_func
    return func(*args, **kwargs)
  File "/mnt/f/data/PC/torch-points-kernels/test/test_fps.py", line 35, in test_gpu
    torch.testing.assert_allclose(sorted_idx,sorted_idx_cpu)
  File "/home/chris/miniconda3/envs/tpk/lib/python3.7/site-packages/torch/testing/_core.py", line 270, in assert_allclose
    raise AssertionError(msg)
AssertionError: Found 27 different element(s) (out of 32), with the greatest difference of 63 (82 vs. 19) occuring at index (8, 1).

[maskjp]

@CCInc , Yes, test_gpu in test_fps.py file is created by me. The original test didn't test the GPU version of fps. I found that the output of the CPU and GPU versions are different even before my modification.

[nicolas-chaulet]

That would make sense, since the seed point might be different. In that case, the test should be modified so that it passes while still checking for some level of correctness. Having test that fails can be a bit confusing.

Le mar. 3 août 2021 à 02:31, maskjp @.***> a écrit :

@CCInc https://github.com/CCInc , Yes, test_gpu in test_fps.py file is created by me. The original test didn't test the GPU version of fps. I found that the output of the CPU and GPU versions are different even before my modification.

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[clee-ai]

Thanks for clarifying! In addition to what Nicolas suggested, would you mind also add a test that verifies the functionality of cuda fps on its own, similar to test_simplecpu?

The rest of the PR works well!