Model Configuration

February 6, 2026 · View on GitHub

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.

NOTE For fields that have comma as the value (e.g. gpu_device_ids, participant_ids), you need to escape the comma with a backslash. For example, if you want to set gpu_device_ids to 0,1 you need to run python3 fill_template.py -i config.pbtxt "gpu_device_ids:0\,1".

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).

logits_datatype The data type for context and generation logits.

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`).
`logits_datatype`	The data type for context and generation logits.

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.
`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.

Optional parameters

Name	Description
`add_special_tokens`	The `add_special_tokens` flag used by HF tokenizers.
`multimodal_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.

multimodal_encoders model

Mandatory parameters

Name	Description
`triton_max_batch_size`	The maximum batch size that Triton should use with the model.
`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.
`multimodal_model_path`	The vision engine path used in multimodal workflow.
`hf_model_path`	The Huggingface model path used for `llava_onevision` and `mllama` models.

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`
`encoder_input_features_data_type`	The dtype for the input tensor `encoder_input_features`. For the mllama model, this must be `TYPE_BF16`. For other models like whisper, this is `TYPE_FP16`.
`logits_datatype`	The data type for context and generation logits.

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=ExecutorConfig::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)
`num_nodes`	Number of MPI nodes to use for this model. (default=1)
`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)
`lora_prefetch_dir`	Folder to store the LoRA weights we hope to load during engine initialization.

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, redrafter, lookahead, eagle} 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. Same applies to the ReDrafter, Lookahead and Eagle.

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, redrafter, lookahead, eagle}` 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. Same applies to the ReDrafter, Lookahead and Eagle.

Optimization

Name	Description
`enable_chunked_context`	Set to `true` to enable context chunking. (default=`false`)
`multi_block_mode`	Set to `false` to disable multi block mode. (default=`true`)
`enable_context_fmha_fp32_acc`	Set to `true` to enable FMHA runner FP32 accumulation. (default=`false`)
`cuda_graph_mode`	Set to `true` to enable cuda graph. (default=`false`)
`cuda_graph_cache_size`	Sets the size of the CUDA graph cache, in numbers of CUDA graphs. (default=0)

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.

Eagle

Name	Description
`eagle_choices`	To specify default per-server Eagle choices tree in the format of e.g. "{0, 0, 0}, {0, 1}". By default, `mc_sim_7b_63` choices are used.

Guided decoding

Name	Description
`guided_decoding_backend`	Set to `xgrammar` to activate guided decoder.
`tokenizer_dir`	The guided decoding of tensorrt_llm python backend requires tokenizer's information.
`xgrammar_tokenizer_info_path`	The guided decoding of tensorrt_llm C++ backend requires xgrammar's tokenizer's info in 'json' format.

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.
`logits_datatype`	The data type for context and generation logits.

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_tokens`	[1]	`int32_t`	Sampling Config param: `minTokens`
`presence_penalty`	[1]	`float`	Sampling Config param: `presencePenalty`
`frequency_penalty`	[1]	`float`	Sampling Config param: `frequencyPenalty`
`seed`	[1]	`uint64_t`	Sampling Config param: `seed`
`return_log_probs`	[1]	`bool`	When `true`, include log probs in the output. Note: This requires at least one sampling parameter to be set (e.g., `runtime_top_k`, `runtime_top_p` for `tensorrt_llm` model, or `top_k`, `top_p` for `tensorrt_llm_bls` model).
`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
`return_perf_metrics`	[1]	`bool`	When `true`, include perf metrics in the output, such as kv cache reuse stats
`guided_decoding_guide_type`	[1]	`string`	Guided decoding param: `guide_type`
`guided_decoding_guide`	[1]	`string`	Guided decoding param: `guide`

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

Note: the timing metrics oputputs are represented as the number of nanoseconds since epoch.

Name	Shape	Type	Description
`cum_log_probs`	[-1]	`float`	Cumulative probabilities for each output
`output_log_probs`	[beam_width, -1]	`float`	Per-token log probabilities for each output. Only returned when `return_log_probs` is `true` and sampling parameters are set.
`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
`kv_cache_alloc_new_blocks`	[1]	`int32`	KV cache reuse metrics. Number of newly allocated blocks per request. Set the optional input `return_perf_metrics` to `true` to include `kv_cache_alloc_new_blocks` in the outputs.
`kv_cache_reused_blocks`	[1]	`int32`	KV cache reuse metrics. Number of reused blocks per request. Set the optional input `return_perf_metrics` to `true` to include `kv_cache_reused_blocks` in the outputs.
`kv_cache_alloc_total_blocks`	[1]	`int32`	KV cache reuse metrics. Number of total allocated blocks per request. Set the optional input `return_perf_metrics` to `true` to include `kv_cache_alloc_total_blocks` in the outputs.
`arrival_time_ns`	[1]	`float`	Time when the request was received by TRT-LLM. Set the optional input `return_perf_metrics` to `true` to include `arrival_time_ns` in the outputs.
`first_scheduled_time_ns`	[1]	`float`	Time when the request was first scheduled. Set the optional input `return_perf_metrics` to `true` to include `first_scheduled_time_ns` in the outputs.
`first_token_time_ns`	[1]	`float`	Time when the first token was generated. Set the optional input `return_perf_metrics` to `true` to include `first_token_time_ns` in the outputs.
`last_token_time_ns`	[1]	`float`	Time when the last token was generated. Set the optional input `return_perf_metrics` to `true` to include `last_token_time_ns` in the outputs.
`acceptance_rate`	[1]	`float`	Acceptance rate of the speculative decoding model. Set the optional input `return_perf_metrics` to `true` to include `acceptance_rate` in the outputs.
`total_accepted_draft_tokens`	[1]	`int32`	Number of tokens accepted by the target model in speculative decoding. Set the optional input `return_perf_metrics` to `true` to include `total_accepted_draft_tokens` in the outputs.
`total_draft_tokens`	[1]	`int32`	Maximum number of draft tokens acceptable by the target model in speculative decoding. Set the optional input `return_perf_metrics` to `true` to include `total_draft_tokens` in the outputs.

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.