Service Startup Parameters

xLLM uses gflags to manage service startup parameters. --model <PATH> is the only required flag. When --config_json_file is used, values in the JSON file override command-line flag values. The tables below are grouped by the Config classes in /xllm/core/framework/config, with one Config per section. The ConfigJsonUtils section contains the common JSON config-file flags.

Device selection: xLLM no longer provides --devices / --device_id / --draft_devices. The available devices are determined by the visible-device mask environment variables (ASCEND_RT_VISIBLE_DEVICES for NPU, CUDA_VISIBLE_DEVICES for NVIDIA, MLU_VISIBLE_DEVICES for Cambricon, HIP_VISIBLE_DEVICES for DCU, MUSA_VISIBLE_DEVICES for Moore Threads). Each service process selects one runtime logical device from its visible devices according to its global node_rank; visible-device subsetting and reordering are resolved by the hardware runtime. The draft model always shares the selected device with the target model.

ConfigJsonUtils

Parameter	Type	Default	Description
config_json_file	string	""	Path to a JSON config file. Values in the file override command-line flag values.
enable_dump_config_json	bool	false	Whether to dump the resolved startup config as JSON.
dump_config_json_file	string	"xllm_config.json"	Path to write the resolved startup config as JSON. Used only when enable_dump_config_json=true.

ServiceConfig

Parameter	Type	Default	Description
host	string	""	Host name or IP for the bRPC server.
port	int32	8010	Port for the bRPC server.
rpc_idle_timeout_s	int32	-1	Close the connection when there are no read/write operations during the last rpc_idle_timeout_s seconds. -1 waits indefinitely.
rpc_channel_timeout_ms	int32	-1	Maximum bRPC Channel duration in milliseconds. -1 waits indefinitely.
max_reconnect_count	int32	40	Maximum number of reconnect attempts from a worker to a server.
num_threads	int32	8	Number of threads used to process requests.
max_concurrent_requests	int32	200	Maximum number of concurrent requests the xLLM instance can handle. Set to 0 for no limit.
num_request_handling_threads	int32	4	Number of threads for handling input requests.
num_response_handling_threads	int32	4	Number of threads for handling responses.
health_check_interval_ms	int32	3000	Worker health-check interval in milliseconds.

ModelConfig

Parameter	Type	Default	Description
model_id	string	""	Hugging Face model name, not a path.
model	string	""	Hugging Face model name or model path.
backend	string	""	Backend model type: llm for text-only models, vlm for multimodal models, or dit for diffusion models.
task	string	"generate"	Model task, for example generate, embed, or mm_embed.
limit_image_per_prompt	int32	8	Maximum number of images per prompt. Only applies to multimodal models.
max_encoder_cache_size	int64	0	Maximum GPU/NPU memory size in MB for the encoder cache per worker. 0 disables the encoder cache.
reasoning_parser	string	""	Reasoning parser, for example auto, glm45, glm47, glm5, qwen3, qwen35, or deepseek-r1.
tool_call_parser	string	""	Tool-call parser, for example auto, qwen25, qwen3, qwen35, qwen3_coder, kimi_k2, deepseekv3, deepseekv32, deepseekv4, glm45, glm47, or glm5.
enable_qwen3_reranker	bool	false	Whether to enable the Qwen3 reranker.
flashinfer_workspace_buffer_size	int32	134217728	Reserved FlashInfer workspace buffer for intermediate attention results in split-k attention. Default is 128 MiB.
enable_return_mm_full_embeddings	bool	false	Whether VLM models return ViT embeddings and sequence embeddings.
mm_download_headers	string	""	Service-level default HTTP headers for multimodal downloads, as a JSON object. Per-request headers take precedence. Example: {"Authorization":"Bearer xxx"}.
use_audio_in_video	bool	false	Whether to decode both audio and video when the input is a video.
use_cpp_chat_template	bool	true	Use native C++ chat templates for supported models, for example deepseek_v32 and deepseek_v4. Set to false to fall back to Jinja for debugging.

LoadConfig

Parameter	Type	Default	Description
enable_manual_loader	bool	false	Pin decoder layer weights to host memory and use async H2D transfer. Required by enable_rolling_load; also implied by enable_xtensor.
enable_rolling_load	bool	false	Enable rolling weight load: keep only N decoder layer weight slots in HBM and stream-load each layer just in time. Requires enable_manual_loader=true. NPU only.
rolling_load_num_cached_layers	int32	2	Number of decoder layer weight slots to keep in HBM when enable_rolling_load=true.
rolling_load_num_rolling_slots	int32	-1	Number of rolling slots used by decoder rolling load. Fixed slots are rolling_load_num_cached_layers - rolling_load_num_rolling_slots. -1 means auto, min(2, preload_count). Must be in [-1, rolling_load_num_cached_layers].
enable_prefetch_weight	bool	false	Whether to enable weight prefetching. Only applies to Qwen3-dense models. The default gateup weight prefetch ratio is 40%; adjust with PREFETCH_COEFFOCIENT.

KVCacheConfig

Parameter	Type	Default	Description
block_size	int32	128	Number of slots per KV Cache block.
max_cache_size	int64	0	Maximum GPU memory size for KV Cache. 0 means calculated from available memory.
max_memory_utilization	double	0.8	Fraction of GPU memory used for model inference, including model weights and KV Cache.
kv_cache_dtype	string	"auto"	KV Cache dtype for quantization. auto aligns with model dtype and disables quantization. int8 enables INT8 quantization and is only supported on the MLU backend.
indexer_cache_dtype	string	"auto"	Indexer cache dtype for models with an indexer cache. Supported values are auto and int8. auto aligns with model dtype and disables indexer cache quantization. int8 enables INT8 indexer cache quantization.
enable_prefix_cache	bool	true	Whether to enable prefix cache in the block manager. See Prefix Cache.
enable_in_batch_prefix_cache	bool	false	Whether to cache admitted prefill full blocks into the prefix cache so that later requests in the same batch can share them.
max_linear_state_cache_slots	int64	0	Maximum number of active linear-attention state cache slots. 0 derives an automatic capacity from the available KV Cache budget.
xxh3_128bits_seed	uint32	1024	Default XXH3 128-bit hash seed.
enable_xtensor	bool	false	Whether to enable XTensor for model weights with the physical page pool.
phy_page_granularity_size	int64	2097152	Granularity size of one physical page in bytes, default 2 MiB, for continuous KV Cache.

KVCacheStoreConfig

Parameter	Type	Default	Description
prefetch_timeout	uint32	0	Stops issuing new KV Cache Store prefetch batches after the timeout and waits for in-flight batches; 0 waits indefinitely.
prefetch_batch_size	uint32	2	Copy batch size for prefetching from KV Cache Store.
layers_wise_copy_batchs	uint32	4	Number of batches for layer-wise H2D copy.
host_blocks_factor	double	0.0	Host block factor, for example host block num = host_blocks_factor * hbm block num.
enable_kvcache_store	bool	false	Whether to enable KV Cache Store.
store_protocol	string	"tcp"	KV Cache Store protocol, for example tcp or rdma.
store_master_server_address	string	""	Store master address. Use IP:Port in standalone mode or etcd://IP:Port;IP:Port;... in etcd-backed HA mode.
store_metadata_server	string	""	Address of the KV Cache Store metadata service.
store_local_hostname	string	""	Local host name of the KV Cache Store client.
enable_control_h2d_block_num	bool	false	Whether to control the number of H2D copy blocks.

BeamSearchConfig

Parameter	Type	Default	Description
enable_beam_search_kernel	bool	false	Whether to enable the beam search kernel.
beam_width	int32	1	Beam width for beam search.
enable_block_copy_kernel	bool	true (NPU/CUDA); false (other backends)	Whether to use the block copy kernel on supported backends.
enable_topk_sorted	bool	true	Whether to enable sorted top-k output.

SchedulerConfig

Parameter	Type	Default	Description
max_tokens_per_batch	int32	10240	Maximum number of tokens per batch.
max_seqs_per_batch	int32	1024	Maximum number of sequences per batch.
enable_schedule_overlap	bool	false	Whether to enable schedule overlap, also known as asynchronous scheduling. See Async Scheduling.
prefill_scheduling_memory_usage_threshold	double	0.95	Memory usage threshold during prefill scheduling.
enable_chunked_prefill	bool	true	Whether to enable chunked prefill.
max_tokens_per_chunk_for_prefill	int32	-1	Maximum number of tokens per chunk in the prefill stage. -1 uses the default policy.
chunked_match_frequency	int32	2	Sequence prefix-cache match frequency.
use_zero_evict	bool	false	Whether to use ZeroEvictionScheduler. See Zero Evict Scheduler.
max_decode_token_per_sequence	int32	256	Maximum decode tokens per sequence for ZeroEvictionScheduler.
priority_strategy	string	"fcfs"	Request priority strategy, for example fcfs, priority, or deadline.
use_mix_scheduler	bool	false	Whether to use MixScheduler to handle prefill and decode uniformly.
enable_online_preempt_offline	bool	true	Whether online requests can preempt offline requests.
aggressive_coeff	double	1.0	Aggressive coefficient for MixScheduler urgency judgment.
starve_threshold	double	1.0	Starvation threshold coefficient for MixScheduler.
enable_starve_prevent	bool	true	Whether to enable anti-starvation behavior in MixScheduler.

ParallelConfig

Parameter	Type	Default	Description
dp_size	int32	1	Data parallel size for MLA attention.
ep_size	int32	1	Expert parallel size for MoE models.
cp_size	int32	1	Context parallel size. Backend and model support is required; 1 disables context parallelism. See Cambricon MLU for MLU-specific constraints.
kv_split_size	int32	1	KV Cache split width. 0 falls back to cp_size (legacy). 1 disables KV split: each CP rank stores the full KV and skips the prefix AllGather. Other K values (K divides cp_size) shard KV across K ranks while token-CP still uses cp_size.
tp_size	int64	1	Tensor parallelism size. Only used for DiT models.
sp_size	int64	1	Sequence parallelism size. Only used for DiT models.
cfg_size	int64	1	Classifier-free guidance parallelism size. Only used for DiT models.
vae_size	int64	1	VAE patch parallelism size. Only used for DiT models.
communication_backend	string	"hccl"	NPU communication backend, for example lccl or hccl. Uses hccl when DP is enabled.
enable_mm_encoder_dp	bool	false	Whether to enable encoder data parallelism for multimodal models.
enable_multi_stream_parallel	bool	false	Whether to enable computation/communication parallelism with two streams and two micro batches in the prefill stage. See Multi-Stream Parallelism.
micro_batch_num	int32	1	Number of micro batches used for multi-stream parallelism.
enable_dp_balance	bool	false	Whether to enable DP load balancing. If true, sequences within a single DP batch are shuffled.

EPLBConfig

Parameter	Type	Default	Description
enable_eplb	bool	false	Whether to enable expert parallel load balance. See EPLB.
redundant_experts_num	int32	1	Number of redundant experts per device.
eplb_update_interval	int64	1000	EPLB update interval.
expert_parallel_degree	int32	0	Expert parallel degree.
rank_tablefile	string	""	ATB HCCL rank table file.

DistributedConfig

Parameter	Type	Default	Description
master_node_addr	string	"127.0.0.1:19888"	Master address for multi-node distributed serving, for example 10.18.1.1:9999.
xtensor_master_node_addr	string	"127.0.0.1:19889"	Master address for the XTensor distributed service, for example 10.18.1.1:9999.
nnodes	int32	1	Number of multi-node nodes.
node_rank	int32	0	Rank of the current node.
etcd_addr	string	""	etcd address used to save instance metadata.
etcd_namespace	string	""	Optional etcd namespace prefix for all xLLM keys, for example prod-a.
enable_service_routing	bool	false	Whether to enable xLLM service routing.
heart_beat_interval	double	0.5	Heartbeat interval.
etcd_ttl	int32	3	Time to live for etcd keys.

DisaggPDConfig

Parameter	Type	Default	Description
enable_disagg_pd	bool	false	Whether to enable disaggregated prefill and decode execution. See P-D Separation.
enable_pd_ooc	bool	false	Whether to enable online-offline co-location in disaggregated PD mode.
disagg_pd_port	int32	7777	Listening port for the disaggregated PD bRPC server.
instance_role	string	"DEFAULT"	Instance role, for example DEFAULT, PREFILL, DECODE, or MIX.
kv_cache_transfer_mode	string	"PUSH"	KV Cache transfer mode, for example PUSH or PULL.
transfer_listen_port	int32	26000	Listening port for KV Cache Transfer.
kv_push_dst_rotate	bool	false	Rotate the destination-worker traversal order in push_kv_blocks per KV-split rank to spread incast across decode workers.

SpeculativeConfig

Parameter	Type	Default	Description
draft_model	string	""	Draft model path. See MTP for MTP usage.
num_speculative_tokens	int32	0	Number of speculative tokens generated per speculative decoding step.
speculative_algorithm	string	"MTP"	Speculative decoding algorithm. Supported values: MTP, Eagle3, Suffix, DFlash, DSpark.
speculative_suffix_cache_max_depth	int32	64	Maximum suffix-tree depth for suffix speculative decoding.
speculative_suffix_max_spec_factor	double	1.0	Maximum suffix speculation token factor relative to match length.
speculative_suffix_max_spec_offset	double	0.0	Maximum additive token offset for suffix speculation.
speculative_suffix_min_token_prob	double	0.1	Minimum token probability used in suffix speculation.
speculative_suffix_max_cached_requests	int32	-1	Maximum number of globally cached requests for suffix speculation. -1 means unlimited; 0 disables it.
speculative_suffix_use_tree_spec	bool	false	Whether to use tree-based suffix speculation instead of path speculation.
draft_sampling_mode	string	"greedy"	How the draft model samples proposal tokens: greedy, probabilistic. Only MTP, DSpark, Eagle3 accept probabilistic.
enable_atb_spec_kernel	bool	false	Whether to use the ATB speculative kernel.

ProfileConfig

Parameter	Type	Default	Description
enable_profile_step_time	bool	false	Whether to enable step-time profiling.
enable_profile_token_budget	bool	false	Whether to enable token-budget profiling.
enable_latency_aware_schedule	bool	false	Whether to use predicted latency for latency-aware scheduling.
profile_max_prompt_length	int32	2048	Maximum prompt length used for profiling.
max_global_ttft_ms	int32	std::numeric_limits<int32_t>::max()	Global TTFT threshold in milliseconds.
max_global_tpot_ms	int32	std::numeric_limits<int32_t>::max()	Global TPOT threshold in milliseconds.
enable_profile_kv_blocks	bool	true	Whether to generate KV Cache blocks for profiling.
disable_ttft_profiling	bool	false	Whether to disable TTFT profiling.
enable_forward_interruption	bool	false	Whether to enable forward interruption.
enable_online_profile	bool	false	Whether to enable the online timeline profiling endpoints (/start_profile and /stop_profile). CUDA only for now; pair with launching the server under nsys --capture-range=cudaProfilerApi.
profile_backend	string	"torch"	Online profiling backend. torch records CPU+CUDA activities in-process and writes a Chrome trace on /stop_profile, no external profiler needed. cuda only toggles the CUDA profiler capture range and requires launching under nsys --capture-range=cudaProfilerApi.
profile_dir	string	""	Directory the torch online profiling backend writes timeline traces to. Empty means the current working directory.

ExecutionConfig

Parameter	Type	Default	Description
enable_graph	bool	false	Whether to enable graph execution for the decode phase to reduce kernel-launch overhead and device idle time. Supports CUDA Graph, ACL Graph (NPU), MLU Graph, and DCU Graph. See Graph Mode.
enable_graph_double_buffer	bool	true	Whether to enable double-buffered ACL graph persistent params and graph instances for NPU schedule-overlap decode.
enable_graph_mode_decode_no_padding	bool	false	Whether decode graph capture uses the actual num_tokens instead of a padded shape.
enable_prefill_piecewise_graph	bool	false	Whether to enable piecewise CUDA graph for the prefill phase. Attention runs in eager mode while other operations are captured in CUDA graphs.
enable_graph_vmm_pool	bool	true	Whether to enable a VMM-backed CUDA graph memory pool for multi-shape graph memory reuse.
max_tokens_for_graph_mode	int32	2048	Maximum number of tokens for graph execution. 0 means no limit.
acl_graph_decode_batch_size_limit	int32	16	Decode batch size threshold for ACL graph on NPU. When the actual decode batch size exceeds this value, ACL graph decode falls back to eager mode to avoid OOM.
enable_shm	bool	false	Whether to enable shared memory for model execution.
use_contiguous_input_buffer	bool	true	Whether to use a contiguous device input buffer for model execution.
input_shm_size	uint64	1024	Input shared-memory size. Default is 1GB.
output_shm_size	uint64	128	Output shared-memory size. Default is 128MB.
random_seed	int32	-1	Random seed for the random number generator. -1 means no fixed seed.

KernelConfig

Parameter	Type	Default	Description
enable_customize_mla_kernel	bool	false	Whether to enable the customized MLA kernel.
npu_kernel_backend	string	"AUTO"	NPU kernel backend. Supported values: AUTO, ATB, TORCH.
enable_intralayer_addnorm	bool	false	Whether to enable fused intralayer addnorm ops.
enable_fused_mc2	int32	-1	Fused MC2 mode for NPU. -1 uses the auto default, 0 disables fused MC2, positive values enable dense matmul-allreduce, 1 uses DispatchFFNCombine for MoE, 2 uses DispatchGmmCombineDecode for MoE.
enable_interlayer_addnorm	bool	false	Whether to enable fused interlayer addnorm ops.
enable_split_rmsnorm_rope	bool	false	Whether to enable fused split rmsnorm rope ops.
enable_aclnn_matmul	bool	false	Whether to enable the ACLNN matmul backend for supported NPU ATB layers.
enable_aclnn_swiglu	bool	false	Whether to enable the ACLNN SwiGLU backend for supported NPU ATB layers.
enable_dspark_native_sas	bool	false	Enable native NPU DSpark SparseAttnSharedkv semantics. Older operators that reject non-empty ori_sparse_indices may terminate during tiling; keep this disabled to use q_len=1 compatibility mode.

DiTConfig

Parameter	Type	Default	Description
max_requests_per_batch	int32	1	Maximum number of requests per batch.
dit_cache_policy	string	"TaylorSeer"	DiT cache policy, for example None, FBCache, TaylorSeer, FBCacheTaylorSeer, or ResidualCache.
dit_cache_warmup_steps	int64	0	Number of warmup steps.
dit_cache_n_derivatives	int64	3	Number of derivatives to use in TaylorSeer.
dit_cache_skip_interval_steps	int64	3	Interval steps to skip for derivative calculation.
dit_cache_residual_diff_threshold	double	0.09	Residual difference threshold for cache reuse.
dit_cache_start_steps	int64	5	Number of steps to skip at the start.
dit_cache_end_steps	int64	5	Number of steps to skip at the end.
dit_cache_start_blocks	int64	5	Number of blocks to skip at the start.
dit_cache_end_blocks	int64	5	Number of blocks to skip at the end.
dit_sp_communication_overlap	bool	true	Whether to overlap communication and computation for sequence parallelism.
dit_debug_print	bool	false	Whether to print debug information for DiT models.
dit_generation_image_area_max	int64	0	Maximum allowed image area (width * height) for image generation requests. 0 means no limit.
dit_enable_vae_tiling	bool	false	Whether to enable VAE tiling. Currently only supported for qwen-image-edit-plus.
dit_vae_image_size	int64	1048576	Qwen-Image-Edit-Plus VAE image size used to calculate dimensions.
dit_sparse_attention_enabled	bool	false	Whether to enable block-wise sparse attention / RainFusion for WAN.
dit_sparse_attention_sparsity	double	0.5	Sparse attention sparsity ratio in [0.0, 1.0). 0.0 means dense attention, 0.5 drops 50 percent of blocks.
dit_sparse_attention_pool_size	int64	128	Sparse attention pooling window size for block-wise mask generation.
dit_sparse_attention_sparse_start_step	int64	0	Sparse attention step index to start sparse attention. Steps before this use dense attention.
dit_sparse_attention_version	string	"rain_fusion"	Sparse attention version: rain_fusion (frame-pairing + aclnnRainFusionAttention) or sparse_attention (block-decompose + aclnnBlockSparseAttention).
dit_sparse_attention_mask_refresh_steps	int64	1	Recompute the block sparse mask every N diffusion steps. 1 means every step, higher values reuse the mask longer.

RecConfig

Parameter	Type	Default	Description
enable_rec_fast_sampler	bool	true	Whether to enable the RecSampler fast sampling path for Rec pipelines.
enable_rec_prefill_only	bool	false	Whether to enable Rec prefill-only mode without decoder self-attention block allocation.
enable_xattention_one_stage	bool	false	Whether to force xattention one-stage decode for Rec multi-round mode.
max_decode_rounds	int32	0	Maximum number of decode rounds for multi-step decoding. 0 means disabled.
enable_constrained_decoding	bool	false	Whether to enable constrained decoding with predefined rules for output format or structure.
output_rec_logprobs	bool	false	Whether to output Rec multi-round token-aligned logprobs. Missing per-token logprobs are filled with the final beam logprob.
enable_convert_tokens_to_item	bool	false	Whether to convert token IDs to item IDs in REC/OneRec responses.
enable_output_sku_logprobs	bool	false	Whether to output REC/OneRec token-aligned logprobs tensors.
enable_extended_item_info	bool	false	Whether to parse and output REC extended item info tensors.
each_conversion_threshold	int32	50	Maximum number of items emitted for each REC token triplet.
total_conversion_threshold	int32	1000	Maximum total number of items emitted in one REC response.
request_queue_size	int32	100000	Scheduler request queue size.
rec_worker_max_concurrency	uint32	1	Concurrency for Rec worker parallel execution. Values less than or equal to 1 disable concurrent Rec workers.