model_config.md

Model Configuration

Model Parameters

The following tables show the parameters in the config.pbtxt of the models in all_models/inflight_batcher_llm. that can be modified before deployment. For optimal performance or custom parameters, please refer to perf_best_practices.

The names of the parameters listed below are the values in the config.pbtxt that can be modified using the fill_template.py script.

The mandatory parameters must be set for the model to run. The optional parameters are not required but can be set to customize the model.

ensemble model

See here to learn more about ensemble models.

Mandatory parameters

Name

Description

triton_max_batch_size

The maximum batch size that the Triton model instance will run with. Note that for the tensorrt_llm model, the actual runtime batch size can be larger than triton_max_batch_size. The runtime batch size will be determined by the TRT-LLM scheduler based on a number of parameters such as number of available requests in the queue, and the engine build trtllm-build parameters (such max_num_tokens and max_batch_size).

preprocessing model

Mandatory parameters

Name	Description
triton_max_batch_size	The maximum batch size that Triton should use with the model.
tokenizer_dir	The path to the tokenizer for the model.
preprocessing_instance_count	The number of instances of the model to run.

Optional parameters

Name	Description
add_special_tokens	The add_special_tokens flag used by HF tokenizers.
visual_model_path	The vision engine path used in multimodal workflow.
engine_dir	The path to the engine for the model. This parameter is only needed for multimodal processing to extract the vocab_size from the engine_dir's config.json for fake_prompt_id mappings.

postprocessing model

Mandatory parameters

Name	Description
triton_max_batch_size	The maximum batch size that Triton should use with the model.
tokenizer_dir	The path to the tokenizer for the model.
postprocessing_instance_count	The number of instances of the model to run.

Optional parameters

Name	Description
skip_special_tokens	The skip_special_tokens flag used by HF detokenizers.

tensorrt_llm model

The majority of the tensorrt_llm model parameters and input/output tensors can be mapped to parameters in the TRT-LLM C++ runtime API defined in executor.h. Please refer to the Doxygen comments in executor.h for a more detailed description of the parameters below.

Mandatory parameters

Name	Description
triton_backend	The backend to use for the model. Set to tensorrtllm to utilize the C++ TRT-LLM backend implementation. Set to python to utlize the TRT-LLM Python runtime.
triton_max_batch_size	The maximum batch size that the Triton model instance will run with. Note that for the tensorrt_llm model, the actual runtime batch size can be larger than triton_max_batch_size. The runtime batch size will be determined by the TRT-LLM scheduler based on a number of parameters such as number of available requests in the queue, and the engine build trtllm-build parameters (such max_num_tokens and max_batch_size).
decoupled_mode	Whether to use decoupled mode. Must be set to true for requests setting the stream tensor to true.
max_queue_delay_microseconds	The maximum queue delay in microseconds. Setting this parameter to a value greater than 0 can improve the chances that two requests arriving within max_queue_delay_microseconds will be scheduled in the same TRT-LLM iteration.
max_queue_size	The maximum number of requests allowed in the TRT-LLM queue before rejecting new requests.
engine_dir	The path to the engine for the model.
batching_strategy	The batching strategy to use. Set to inflight_fused_batching when enabling in-flight batching support. To disable in-flight batching, set to V1

Optional parameters

• General

Name	Description
encoder_engine_dir	When running encoder-decoder models, this is the path to the folder that contains the model configuration and engine for the encoder model.
max_attention_window_size	When using techniques like sliding window attention, the maximum number of tokens that are attended to generate one token. Defaults attends to all tokens in sequence. (default=max_sequence_length)
sink_token_length	Number of sink tokens to always keep in attention window.
exclude_input_in_output	Set to true to only return completion tokens in a response. Set to false to return the prompt tokens concatenated with the generated tokens. (default=false)
cancellation_check_period_ms	The time for cancellation check thread to sleep before doing the next check. It checks if any of the current active requests are cancelled through triton and prevent further execution of them. (default=100)
stats_check_period_ms	The time for the statistics reporting thread to sleep before doing the next check. (default=100)
recv_poll_period_ms	The time for the receiving thread in orchestrator mode to sleep before doing the next check. (default=0)
iter_stats_max_iterations	The maximum number of iterations for which to keep statistics. (default=executor::kDefaultIterStatsMaxIterations)
request_stats_max_iterations	The maximum number of iterations for which to keep per-request statistics. (default=executor::kDefaultRequestStatsMaxIterations)
normalize_log_probs	Controls if log probabilities should be normalized or not. Set to false to skip normalization of output_log_probs. (default=true)
gpu_device_ids	Comma-separated list of GPU IDs to use for this model. Use semicolons to separate multiple instances of the model. If not provided, the model will use all visible GPUs. (default=unspecified)
participant_ids	Comma-separated list of MPI ranks to use for this model. Mandatory when using orchestrator mode with -disable-spawn-process (default=unspecified)
gpu_weights_percent	Set to a number between 0.0 and 1.0 to specify the percentage of weights that reside on GPU instead of CPU and streaming load during runtime. Values less than 1.0 are only supported for an engine built with weight_streaming on. (default=1.0)

• KV cache

Note that the parameter enable_trt_overlap has been removed from the config.pbtxt. This option allowed to overlap execution of two micro-batches to hide CPU overhead. Optimization work has been done to reduce the CPU overhead and it was found that the overlapping of micro-batches did not provide additional benefits.

Name	Description
max_tokens_in_paged_kv_cache	The maximum size of the KV cache in number of tokens. If unspecified, value is interpreted as 'infinite'. KV cache allocation is the min of max_tokens_in_paged_kv_cache and value derived from kv_cache_free_gpu_mem_fraction below. (default=unspecified)
kv_cache_free_gpu_mem_fraction	Set to a number between 0 and 1 to indicate the maximum fraction of GPU memory (after loading the model) that may be used for KV cache. (default=0.9)
cross_kv_cache_fraction	Set to a number between 0 and 1 to indicate the maximum fraction of KV cache that may be used for cross attention, and the rest will be used for self attention. Optional param and should be set for encoder-decoder models ONLY. (default=0.5)
kv_cache_host_memory_bytes	Enable offloading to host memory for the given byte size.
enable_kv_cache_reuse	Set to true to reuse previously computed KV cache values (e.g. for system prompt)

• LoRA cache

Name	Description
lora_cache_optimal_adapter_size	Optimal adapter size used to size cache pages. Typically optimally sized adapters will fix exactly into 1 cache page. (default=8)
lora_cache_max_adapter_size	Used to set the minimum size of a cache page. Pages must be at least large enough to fit a single module, single later adapter_size maxAdapterSize row of weights. (default=64)
lora_cache_gpu_memory_fraction	Fraction of GPU memory used for LoRA cache. Computed as a fraction of left over memory after engine load, and after KV cache is loaded. (default=0.05)
lora_cache_host_memory_bytes	Size of host LoRA cache in bytes. (default=1G)

• Decoding mode

Name	Description
max_beam_width	The beam width value of requests that will be sent to the executor. (default=1)
decoding_mode	Set to one of the following: {top_k, top_p, top_k_top_p, beam_search, medusa} to select the decoding mode. The top_k mode exclusively uses Top-K algorithm for sampling, The top_p mode uses exclusively Top-P algorithm for sampling. The top_k_top_p mode employs both Top-K and Top-P algorithms, depending on the runtime sampling params of the request. Note that the top_k_top_p option requires more memory and has a longer runtime than using top_k or top_p individually; therefore, it should be used only when necessary. beam_search uses beam search algorithm. If not specified, the default is to use top_k_top_p if max_beam_width == 1; otherwise, beam_search is used. When Medusa model is used, medusa decoding mode should be set. However, TensorRT-LLM detects loaded Medusa model and overwrites decoding mode to medusa with warning.

• Optimization

Name	Description
enable_chunked_context	Set to true to enable context chunking. (default=false)

• Scheduling

Name	Description
batch_scheduler_policy	Set to max_utilization to greedily pack as many requests as possible in each current in-flight batching iteration. This maximizes the throughput but may result in overheads due to request pause/resume if KV cache limits are reached during execution. Set to guaranteed_no_evict to guarantee that a started request is never paused. (default=guaranteed_no_evict)

• Medusa

Name	Description
medusa_choices	To specify Medusa choices tree in the format of e.g. "{0, 0, 0}, {0, 1}". By default, mc_sim_7b_63 choices are used.

tensorrt_llm_bls model

See here to learn more about BLS models.

Mandatory parameters

Name	Description
triton_max_batch_size	The maximum batch size that the model can handle.
decoupled_mode	Whether to use decoupled mode.
bls_instance_count	The number of instances of the model to run. When using the BLS model instead of the ensemble, you should set the number of model instances to the maximum batch size supported by the TRT engine to allow concurrent request execution.

Optional parameters

• General

Name	Description
accumulate_tokens	Used in the streaming mode to call the postprocessing model with all accumulated tokens, instead of only one token. This might be necessary for certain tokenizers.

• Speculative decoding

The BLS model supports speculative decoding. Target and draft triton models are set with the parameters tensorrt_llm_model_name tensorrt_llm_draft_model_name. Speculative decodingis performed by setting num_draft_tokens in the request. use_draft_logits may be set to use logits comparison speculative decoding. Note that return_generation_logits and return_context_logits are not supported when using speculative decoding. Also note that requests with batch size greater than 1 is not supported with speculative decoding right now.

Name	Description
tensorrt_llm_model_name	The name of the TensorRT-LLM model to use.
tensorrt_llm_draft_model_name	The name of the TensorRT-LLM draft model to use.

Model Input and Output

Below is the lists of input and output tensors for the tensorrt_llm and tensorrt_llm_bls models.

Common Inputs

Name	Shape	Type	Description
end_id	[1]	int32	End token ID. If not specified, defaults to -1
pad_id	[1]	int32	Padding token ID
temperature	[1]	float32	Sampling Config param: temperature
repetition_penalty	[1]	float	Sampling Config param: repetitionPenalty
min_length	[1]	int32_t	Sampling Config param: minLength
presence_penalty	[1]	float	Sampling Config param: presencePenalty
frequency_penalty	[1]	float	Sampling Config param: frequencyPenalty
random_seed	[1]	uint64_t	Sampling Config param: randomSeed
return_log_probs	[1]	bool	When true, include log probs in the output
return_context_logits	[1]	bool	When true, include context logits in the output
return_generation_logits	[1]	bool	When true, include generation logits in the output
num_return_sequences	[1]	int32_t	Number of generated sequences per request. (Default=1)
beam_width	[1]	int32_t	Beam width for this request; set to 1 for greedy sampling (Default=1)
prompt_embedding_table	[1]	float16 (model data type)	P-tuning prompt embedding table
prompt_vocab_size	[1]	int32	P-tuning prompt vocab size

The following inputs for lora are for both tensorrt_llm and tensorrt_llm_bls models. The inputs are passed through the tensorrt_llm model and the tensorrt_llm_bls model will refer to the inputs from the tensorrt_llm model.

Name	Shape	Type	Description
lora_task_id	[1]	uint64	The unique task ID for the given LoRA. To perform inference with a specific LoRA for the first time, lora_task_id, lora_weights, and lora_config must all be given. The LoRA will be cached, so that subsequent requests for the same task only require lora_task_id. If the cache is full, the oldest LoRA will be evicted to make space for new ones. An error is returned if lora_task_id is not cached
lora_weights	[ num_lora_modules_layers, D x Hi + Ho x D ]	float (model data type)	Weights for a LoRA adapter. See the config file for more details.
lora_config	[ num_lora_modules_layers, 3]	int32t	Module identifier. See the config file for more details.

Common Outputs

Name	Shape	Type	Description
cum_log_probs	[-1]	float	Cumulative probabilities for each output
output_log_probs	[beam_width, -1]	float	Log probabilities for each output
context_logits	[-1, vocab_size]	float	Context logits for input
generation_logits	[beam_width, seq_len, vocab_size]	float	Generation logits for each output
batch_index	[1]	int32	Batch index

Unique Inputs for tensorrt_llm model

Name	Shape	Type	Description
input_ids	[-1]	int32	Input token IDs
input_lengths	[1]	int32	Input lengths
request_output_len	[1]	int32	Requested output length
draft_input_ids	[-1]	int32	Draft input IDs
decoder_input_ids	[-1]	int32	Decoder input IDs
decoder_input_lengths	[1]	int32	Decoder input lengths
draft_logits	[-1, -1]	float32	Draft logits
draft_acceptance_threshold	[1]	float32	Draft acceptance threshold
stop_words_list	[2, -1]	int32	List of stop words
bad_words_list	[2, -1]	int32	List of bad words
embedding_bias	[-1]	string	Embedding bias words
runtime_top_k	[1]	int32	Top-k value for runtime top-k sampling
runtime_top_p	[1]	float32	Top-p value for runtime top-p sampling
runtime_top_p_min	[1]	float32	Minimum value for runtime top-p sampling
runtime_top_p_decay	[1]	float32	Decay value for runtime top-p sampling
runtime_top_p_reset_ids	[1]	int32	Reset IDs for runtime top-p sampling
len_penalty	[1]	float32	Controls how to penalize longer sequences in beam search (Default=0.f)
early_stopping	[1]	bool	Enable early stopping
beam_search_diversity_rate	[1]	float32	Beam search diversity rate
stop	[1]	bool	Stop flag
streaming	[1]	bool	Enable streaming

Unique Outputs for tensorrt_llm model

Name	Shape	Type	Description
output_ids	[-1, -1]	int32	Output token IDs
sequence_length	[-1]	int32	Sequence length

Unique Inputs for tensorrt_llm_bls model

Name	Shape	Type	Description
text_input	[-1]	string	Prompt text
decoder_text_input	[1]	string	Decoder input text
image_input	[3, 224, 224]	float16	Input image
max_tokens	[-1]	int32	Number of tokens to generate
bad_words	[2, num_bad_words]	int32	Bad words list
stop_words	[2, num_stop_words]	int32	Stop words list
top_k	[1]	int32	Sampling Config param: topK
top_p	[1]	float32	Sampling Config param: topP
length_penalty	[1]	float32	Sampling Config param: lengthPenalty
stream	[1]	bool	When true, stream out tokens as they are generated. When false return only when the full generation has completed (Default=false)
embedding_bias_words	[-1]	string	Embedding bias words
embedding_bias_weights	[-1]	float32	Embedding bias weights
num_draft_tokens	[1]	int32	Number of tokens to get from draft model during speculative decoding
use_draft_logits	[1]	bool	Use logit comparison during speculative decoding

Unique Outputs for tensorrt_llm_bls model

Name	Shape	Type	Description
text_output	[-1]	string	Text output

Some tips for model configuration

Below are some tips for configuring models for optimal performance. These recommendations are based on our experiments and may not apply to all use cases. For guidance on other parameters, please refer to the perf_best_practices.

• Setting the instance_count for models to better utilize inflight batching

  The instance_count parameter in the config.pbtxt file specifies the number of instances of the model to run. Ideally, this should be set to match the maximum batch size supported by the TRT engine, as this allows for concurrent request execution and reduces performance bottlenecks. However, it will also consume more CPU memory resources. While the optimal value isn't something we can determine in advance, it generally shouldn't be set to a very small value, such as 1. For most use cases, we have found that setting instance_count to 5 works well across a variety of workloads in our experiments.

• Adjusting max_batch_size and max_num_tokens to optimize inflight batching

  max_batch_size and max_num_tokens are important parameters for optimizing inflight batching. You can modify max_batch_size in the model configuration file, while max_num_tokens is set during the conversion to a TRT-LLM engine using the trtllm-build command. Tuning these parameters is necessary for different scenarios, and experimentation is currently the best approach to finding optimal values. Generally, the total number of requests should be lower than max_batch_size, and the total tokens should be less than max_num_tokens.