Fix LongRoPE KV Cache #1
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Issue
Before this fix: if we start from a prompt with length < 4K but the total sequence length will >4K after generation, the generated tokens after 4K will be gabage.
Root Cause
LongRoPE uses difference scaling factors for <=4k / > 4k sequences. When the generation comes across the switch point of 4K, the kv cache of prefill tokens are calculated based on short factors, but the new tokens are generated based on long factors. This inconsistency leads to the generation crash.
Solution
Pass
prompt_length + max_generation_tokensto the model.If it is larger than 4K, we should use the long factors for all calculations of this sequence.