Fix allreduce for BF16 and ZeRO0 #5170
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tjruwase
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Feb 21, 2024
ShellyNR
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Mar 11, 2024
This PR fixes an issue with allreducing for ZeRO0 + BF16. (This replaces microsoft#5154) DeepSpeed uses `BF16_Optimizer` when ZeRO0 and BF16 are enabled. The optimizer accumulates gradients on FP32 buffer soon after a backward pass completes. However, DeepSpeed engine performs allreduce on BF16 gradients. This PR fixes the issue by performing allreduce on the FP32 buffer. It also eliminates an assertion that prohibits BF16+PP+Z1, which is actually runnable. This shows loss curves of the following conditions: - BF16/Z0,Z1,Z2,Z3/NoPP - BF16/Z0,Z1/PP(2 stages) (all used 8GPUs, gradient accumulation step: 4)  --------- Co-authored-by: Logan Adams <[email protected]>
rraminen
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May 9, 2024
This PR fixes an issue with allreducing for ZeRO0 + BF16. (This replaces microsoft#5154) DeepSpeed uses `BF16_Optimizer` when ZeRO0 and BF16 are enabled. The optimizer accumulates gradients on FP32 buffer soon after a backward pass completes. However, DeepSpeed engine performs allreduce on BF16 gradients. This PR fixes the issue by performing allreduce on the FP32 buffer. It also eliminates an assertion that prohibits BF16+PP+Z1, which is actually runnable. This shows loss curves of the following conditions: - BF16/Z0,Z1,Z2,Z3/NoPP - BF16/Z0,Z1/PP(2 stages) (all used 8GPUs, gradient accumulation step: 4)  --------- Co-authored-by: Logan Adams <[email protected]>
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This PR fixes an issue with allreducing for ZeRO0 + BF16. (This replaces #5154)
DeepSpeed uses
BF16_Optimizerwhen ZeRO0 and BF16 are enabled. The optimizer accumulates gradients on FP32 buffer soon after a backward pass completes. However, DeepSpeed engine performs allreduce on BF16 gradients.This PR fixes the issue by performing allreduce on the FP32 buffer. It also eliminates an assertion that prohibits BF16+PP+Z1, which is actually runnable.
This shows loss curves of the following conditions:
(all used 8GPUs, gradient accumulation step: 4)