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tohtana merged 3 commits into from
Mar 4, 2026
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Add comment explaining nesting torch.autocast #1000

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Add comment explaining outer torch.autocast in bf16_master_weight exa…
tohtana Mar 4, 2026
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Merge branch 'master' into doc-autocast-nesting
tohtana Mar 4, 2026
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Update training/bf16_master_weight/train.py
tohtana Mar 4, 2026
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6 changes: 5 additions & 1 deletion training/bf16_master_weight/train.py
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Expand Up @@ -292,7 +292,11 @@ def main():
input_ids = torch.randint(0, actual_vocab_size, (args.batch_size, args.seq_length), device=device)
labels = torch.randint(0, actual_vocab_size, (args.batch_size, args.seq_length), device=device)

# Forward pass with optional autocast
# Forward pass with optional autocast.
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# DeepSpeed already applies torch.autocast inside engine.forward(), but
# we wrap the entire forward+loss block so that loss_fn also runs under
# autocast. The nested autocast on engine.forward() is harmless —
# PyTorch's torch.autocast is idempotent when nested with the same dtype.
if use_autocast:
with torch.autocast(device_type="cuda", dtype=autocast_dtype):
logits = model_engine(input_ids)
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