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Updating the Flash Attention version to fix cross entropy loss #812
Merged
ShashankMosaicML
merged 21 commits into
mosaicml:main
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ShashankMosaicML:shashank/update_FA_version_fix_CE
Dec 20, 2023
Merged
Updating the Flash Attention version to fix cross entropy loss #812
ShashankMosaicML
merged 21 commits into
mosaicml:main
from
ShashankMosaicML:shashank/update_FA_version_fix_CE
Dec 20, 2023
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Pulling the latest commits from main fork
Pulling from the main repo
Pulling from mosaicml/llm-foundry main
Merging from mosaic main
Pulling from mosaic main
Pulling from mosaic main.
dakinggg
reviewed
Dec 19, 2023
dakinggg
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Dec 20, 2023
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LGTM, please add a PR description explaining stuff
Done. |
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The cross entropy loss of Flash Attention v2.3.2 (and lower) throws illegal memory access error when used with large (device train microbatch size X sequence length X vocabulary). To fix this we had reverted back to FA v1's CE loss in this PR (#795). However, we discovered that for very large (device train microbatch size X sequence length X vocabulary), FA v1's CE loss runs into numerical precision errors, causing divergence.
The newer versions of Flash Attention (v2.3.3 and higher) seem to have solved both of these problems, and hence in this PR, we update the repo to start using FA v2.3.6 (the latest version) instead of FA v2.3.2.
The blue loss curve below corresponds to the training run using FA v2.3.6's CE loss, and the pink curve corresponds to training run using FA v1's CE loss.