[Frontend] Set server's maximum number of generated tokens using generation_config.json #12242
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ModelConfig.get_diff_sampling_params() now allows for reading the "max_new_tokens" if its specified in the generation_config.json file. This follows Huggingface's naming convention for the variable that specifies the maximum number of generated tokens. This gets renamed to "max_tokens" to follow the naming convention used by vLLM for the same functionality.
Previously the default_max_tokens was the (max_model_len - prompt_tokens), but now the server_max_tokens = min( max_model_len - prompt_tokens, max_tokens if set in generation_config.json )
server_max_tokens is the minimum between architectural limitations, which was the default_max_tokens, and max_new_tokens set in generation_config.json
I have int's so that wasn't good. I could have gone with 2**64 or something, but didn't like the idea of some hardcoded value. So changed a logic just a touch.
Also added in setting server_max_tokens to the minimum of context window - prompt and the value of max_new_tokens set in generation_config.json
server_max_tokens is set either by architectural limits (context_window - prompt_tokens) or max_new_tokens value set in generation_config.json
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DarkLight1337
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This PR adds in the ability to specify the
max_new_tokensentry in the generation_config.json file. Setting this parameter will act as the server's maximum number of generated tokens any given request can have.If a user does not specify a
max_tokensin their request, then the minimum ofmax_new_tokensand (max_model_len- prompt_tokens) will be used. Current behavior just uses themax_model_len- prompt_tokens as a default. For large context window models, e.g., Llama-3.1, this is 128K.If a user does specify a
max_tokens, then the minimum ofmax_tokens,max_new_tokens, ormax_model_len- prompt_tokens will be used. Current behavior allows user to specifymax_tokenslarger than is physically allowed by the context window, though it will throw an error. Now it would quietly override user's requestedmax_tokens.Still need to add some testing, but would appreciate some pointers to where the tests should be added. @DarkLight1337 suggested it may not be necessary to update the
vllm/entrypoints/llm.py, but I've left that in for now until final determination can be made.FIX #11976