leezu commented on issue #17530: Add deferred compute support URL: https://github.com/apache/incubator-mxnet/pull/17530#issuecomment-590473083 @eric-haibin-lin enabling deferred compute mode enables recording and deferring the computation. It does not automatically export the recording to a CachedOp and use that for accelerated computation. This logic is implemented in `HybridBlock.__call__`. `HybridBlock.__call__`, which automatically enables deferred compute mode for the computation of the Block. Users should not enable deferred compute outside manually (in fact it's an internal API as of this PR). We can add a `@hyridize` decorator in the future, which helps to hybridize functions based on deferred compute. Specifically to your code example, there are a few more considerations: **Cross device execution** `copyto` is not supported by CachedOp yet. Thus while we can use `copyto` inside deferred compute mode, exporting to Symbol and running the Symbol will fail. **Autograd** Autograd recording and deferred compute recording are currently mutually exclusive. You can't enable both at the same time. But you don't need to: Deferred compute provides the symbolic representation of the forward computation. We don't need autograd while obtaining this symbolic representation, ie. we can just disable autograd inside the deferred compute scope. `CachedOp` takes the symbol and facilitates computing gradients. It will be useful to support autograd inside deferred compute in the future, for higher order grads. > what happens if a user enables DC for the program below? `MXNetError("Autograd recording is not supported during deferred compute mode.")` https://github.com/apache/incubator-mxnet/blob/e64e03cb27b43f369c27c6629f1238103fa875e0/src/imperative/imperative.cc#L204-L214 https://github.com/apache/incubator-mxnet/blob/e64e03cb27b43f369c27c6629f1238103fa875e0/src/imperative/imperative.cc#L295-L299
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