Add nvprims.var_mean (#83508)
This PR adds nvfuser-specific primitive - `var_mean`.
Interpretation `torch.var_mean` -> `torch.ops.nvprims.var_mean` is handled by `TorchRefsNvfuserCapabilityMode` context manager.
I moved some helper code from `_prims/__init__.py` to `_prims_common`. Correctness is tested with OpInfo tests (see `PythonRefInfo("ops.nvprims.var_mean"`).
Layer norm reference now uses `torch.var_mean` instead of `torch._refs.var_mean` to allow interception. Here's a simple comparison of performance with this PR and master (on 3080ti):
```py
import torch
from torch._prims.context import TorchRefsNvfuserCapabilityMode
from torch.fx.experimental.proxy_tensor import make_fx
from torch._prims.executor import execute
def func(a):
return torch.native_layer_norm(a, (1024,), None, None, 1e-6)
a = torch.randn(10, 512, 1024, dtype=torch.float16, device="cuda")
with TorchRefsNvfuserCapabilityMode():
gm = make_fx(func)(a)
for _ in range(10):
execute(gm, a, executor="strictly_nvfuser");
```
run with `PYTORCH_NVFUSER_DUMP=dump_eff_bandwidth python script.py`
```py
# WITH THIS PR
# kernel1 run in 0.032768 ms, achieved: 641.25 GB/s
# kernel1 run in 0.033792 ms, achieved: 621.818 GB/s
# kernel1 run in 0.032768 ms, achieved: 641.25 GB/s
# kernel1 run in 0.032608 ms, achieved: 644.396 GB/s
# kernel1 run in 0.031744 ms, achieved: 661.935 GB/s
# kernel1 run in 0.031744 ms, achieved: 661.935 GB/s
# kernel1 run in 0.032768 ms, achieved: 641.25 GB/s
# kernel1 run in 0.03072 ms, achieved: 684 GB/s
# kernel1 run in 0.031744 ms, achieved: 661.935 GB/s
# kernel1 run in 0.031744 ms, achieved: 661.935 GB/s
# ON MASTER
# kernel1 run in 0.05632 ms, achieved: 373.091 GB/s
# kernel1 run in 0.044032 ms, achieved: 477.209 GB/s
# kernel1 run in 0.044032 ms, achieved: 477.209 GB/s
# kernel1 run in 0.044032 ms, achieved: 477.209 GB/s
# kernel1 run in 0.043808 ms, achieved: 479.649 GB/s
# kernel1 run in 0.043008 ms, achieved: 488.571 GB/s
# kernel1 run in 0.044032 ms, achieved: 477.209 GB/s
# kernel1 run in 0.043008 ms, achieved: 488.571 GB/s
# kernel1 run in 0.043008 ms, achieved: 488.571 GB/s
# kernel1 run in 0.043008 ms, achieved: 488.571 GB/s
```
So this PR gives about 35% improvement in performance using nvfuser executor with this specific normalized shape.
Also this PR fixes https://github.com/pytorch/pytorch/issues/83506 (see the change in `torch/csrc/jit/python/pybind_utils.cpp`).
Ref. https://github.com/pytorch/pytorch/issues/80187
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83508
Approved by: https://github.com/ngimel