Do not prefetch when possible #12101
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carmocca
commented
Feb 25, 2022
carmocca
requested review from
Borda,
tchaton,
SeanNaren,
awaelchli,
justusschock,
williamFalcon,
kaushikb11 and
rohitgr7
as code owners
kaushikb11
reviewed
Feb 28, 2022
justusschock
approved these changes
Feb 28, 2022
rohitgr7
approved these changes
Feb 28, 2022
| @@ -393,6 +393,9 @@ option when using sequential data. | |||
| to ``limit_{mode}_batches``, if it is set to 1.0 it will run for the whole dataset, otherwise it will throw an exception. | |||
| Here ``mode`` can be train/val/test/predict. | |||
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| When iterable datasets are used, Lightning will pre-fetch 1 batch (in addition to the current batch) so it can detect | |||
| when the training will stop and run validation if necessary. | |||
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| when the training will stop and run validation if necessary. | |
| when the training epoch will end and run validation if necessary. |
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while the comment here is not wrong, the real reason we have the prefetching is actually to avoid starting a new epoch that doesn't have any batches left in the dataloader. Relying on a StopIteration check is not possible for this reason.
Co-authored-by: Rohit Gupta <rohitgr1998@gmail.com>
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What does this PR do?
Only prefetch unless we require it. That is when:
This is good for FFCV because they already do prefetching internally.
We no longer error on 0-length map-style datasets as this is inconsistent with iterable datasets.
Part of #11538
Follow-up to #11606
Reverts #1280
Does your PR introduce any breaking changes? If yes, please list them.
None knowingly
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cc @Borda @justusschock @awaelchli @ninginthecloud @akihironitta