The way the aot autograd sequence_nr tracking works is that we run the aot export logic, the dynamo captured forward graph is run under an fx.Interpreter, which iterates through the nodes of the forward graph while setting the `current_metadata`.
Since during backward what is run doesn't correspond to any node during forward, we fallback to the global `current_metadata`. And since this global metadata is ends up being shared between runs, that leads to weirdness if we forget to reset things, e.g., depending whether this is the first test run, the printed results will be different.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107210
Approved by: https://github.com/bdhirsh
Fixes#102375
Sequence_nr increments in the forward pass and decrements in the backward pass. Backward ops with the same sequence_nr as a forward op represent the backward implementation for the op. The long term goal is to make this information available to the profiler so users can observe which ops are fused by the inductor openai triton kernels.
Added a test for this feature **test/dynamo/test_aot_autograd.py::AotAutogradFallbackTests::test_aot_sequence_nr**. The test case uses **aot_export_module()** to create a joint fwd/bwd fx graph. Then it walks all the nodes in fx graph using fx_graph.graph.nodes. The seq_nr of each node is recorded in node.meta. During the fwd pass the seq_nr increments and it decrements during the bwd pass. This allows the user to map forward ops to their corresponding bwd ops which is useful for performance analysis.
Expected output from the test case.
SeqNr|OrigAten|SrcFn
0|aten.convolution.default|l__self___conv1
0|aten.add.Tensor|l__self___bn1
1|aten._native_batch_norm_legit_functional.default|l__self___bn1
2|aten.relu.default|l__self___relu1
3|aten.add.Tensor|add
4|aten.view.default|flatten
5|aten.t.default|l__self___fc1
6|aten.unsqueeze.default|l__self___fc1
7|aten.mm.default|l__self___fc1
8|aten.squeeze.dim|l__self___fc1
9|aten.add.Tensor|l__self___fc1
10|aten.sub.Tensor|l__self___loss_fn
11|aten.abs.default|l__self___loss_fn
12|aten.mean.default|l__self___loss_fn
12|aten.ones_like.default|
12|aten.expand.default|
12|aten.div.Scalar|
11|aten.sgn.default|
11|aten.mul.Tensor|
8|aten.unsqueeze.default|
7|aten.t.default|
7|aten.mm.default|
7|aten.t.default|
7|aten.t.default|
7|aten.mm.default|
6|aten.squeeze.dim|
5|aten.t.default|
4|aten.view.default|
2|aten.threshold_backward.default|
1|aten.native_batch_norm_backward.default|
0|aten.convolution_backward.default|
0|aten.add.Tensor|
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103129
Approved by: https://github.com/soulitzer
