evalstone/evalscope/docs/en/user_guides/stress_test/parameters.md

Parameter

Execute evalscope perf --help to get a full parameter description.

Basic Settings

Parameter	Type	Description	Default
--model	str	Name or path of the test model	-
--url	str	API address, supporting /chat/completions, /completions, and /responses endpoints	-
--name	str	Name for wandb/swanlab database result and result database	{model_name}_{current_time}
--api	str	Service API type • openai: OpenAI-compatible Chat Completions API (requires --url) • openai_responses: OpenAI official Responses API • openai_embedding: OpenAI-compatible Embedding API • openai_rerank: OpenAI/Cohere-compatible Rerank API • local: Start local transformers inference • local_vllm: Start local vLLM inference service • Custom: See Custom API Guide	-
--port	int	Port for local inference service Only applicable to local and local_vllm	8877
--attn-implementation	str	Attention implementation method Only effective when api=local	None (Optional: flash_attention_2, eager, sdpa)
--api-key	str	API key	None
--debug	bool	Whether to output debug information	False

Network Configuration

Parameter	Type	Description	Default
--total-timeout	int	Total timeout for each request (seconds)	21600 (6 hours)
--connect-timeout	int	Network connection timeout (seconds)	None
--read-timeout	int	Network read timeout (seconds)	None
--headers	str	Additional HTTP headers Format: key1=value1 key2=value2 Will be used for each query	-
--no-test-connection	bool	Do not send connection test, start stress test directly	False

Request Control

Parameter	Type	Description	Default
--parallel	list[int]	Number of concurrent requests Can input multiple values separated by spaces	1
--number	list[int]	Total number of requests to be sent Can input multiple values (must correspond one-to-one with parallel)	1000
--rate	float	Request scheduling rate (requests/second) • -1: No rate pacing; in the default closed-loop mode, requests are scheduled as fast as possible, but the number of in-flight HTTP requests is still capped by --parallel, so requests are not all sent to the server at once • > 0: Requests are scheduled following a Poisson arrival model — the inter-arrival interval follows an exponential distribution with mean 1/rate, resulting in an average of rate scheduled requests per second	-1
--log-every-n-query	int	Log every N queries	100
--stream	bool	Whether to use SSE stream output Must be enabled to measure TTFT (Time to First Token) metric	True
--sleep-interval	int	Sleep time between each performance test (seconds) Helps avoid overloading the server	5
--open-loop	bool	Enable open-loop mode: dispatch requests following a Poisson arrival schedule without semaphore backpressure. Requests are fired at the rate set by --rate regardless of whether the server has finished processing previous requests. • --rate becomes the sweep variable (accepts multiple values), replacing --parallel to drive multi-run iterations • --number must have the same length as --rate; each pair (rate, number) corresponds to one independent run • --parallel is ignored in this mode (internally set to -1 / INF) See Usage Example	False
--warmup-num	float	Number or ratio of warmup requests: • 0: disabled (default) • >= 1: absolute count, e.g. --warmup-num 10 sends 10 warmup requests • 0 < value < 1: ratio mode, e.g. --warmup-num 0.1 = 10% of --number Warmup requests are sent with the same concurrency/rate as the benchmark but excluded from performance metrics Useful for eliminating cold-start effects (KV-cache filling, JIT compilation, etc.) In closed-loop mode, set it to --parallel or more, otherwise the first few requests inflate p99 See Usage Example	0
--duration	float	Wall-clock budget for one benchmark run (seconds) Soft-exit semantics: once the deadline elapses no new requests are dispatched, but already in-flight requests are allowed to finish before exit In multi-turn mode "in-flight" means already-claimed traces run every remaining turn (trace-level soft exit, aligned with upstream trie) When combined with --number, whichever cap is hit first ends the run	None

**Closed-loop (default)** vs **Open-loop** (`--open-loop`) — parameter behaviour comparison:

| | Closed-loop (default) | Open-loop (`--open-loop`) |
|---|---|---|
| **`--rate`** | Controls request scheduling rate (`-1` = no pacing, but still bounded by the `--parallel` concurrency cap; `R` = Poisson-arrival mean) | Controls dispatch rate; **must be > 0**; accepts multiple values (e.g. `5 10 20`), each driving one independent run |
| **`--number`** | Total requests per run; must match `--parallel` in length | Total requests per run; must match `--rate` in **length** |
| **`--parallel`** | Max in-flight requests; each worker waits for a response before sending the next (**backpressure**) | **Ignored**; concurrency is unbounded (INF); requests are fired on schedule without waiting for responses |
| **Use case** | Measure latency and throughput under controlled concurrency | Simulate realistic traffic (arrivals independent of service time); sweep throughput-latency curve across multiple rates |

SLA Settings

Parameter	Type	Description	Default
--sla-auto-tune	bool	Whether to enable SLA auto-tuning mode	False
--sla-variable	str	Variable for auto-tuning Options: parallel (concurrency), rate (request rate)	parallel
--sla-params	str	SLA constraint conditions JSON string Supported metrics: avg_latency, p99_latency, avg_ttft, p99_ttft, avg_tpot, p99_tpot, rps, tps Supported operators: <=, <, min (for latency metrics); >=, >, max (for throughput metrics) Example: '[{"p99_latency": "<=2"}]'	None
--sla-upper-bound	int	Upper bound of the tuned SLA variable search range	65536
--sla-lower-bound	int	Lower bound of the tuned SLA variable search range	1
--sla-fixed-parallel	int	Fixed parallel workers used when --sla-variable=rate; defaults to --sla-upper-bound for backward compatibility	None
--sla-num-runs	int	Number of runs per concurrency level (average taken)	3
--sla-number-multiplier	float	Multiplier of total requests relative to the tuned variable (concurrency or rate), i.e. number = round(variable × N); defaults to 2 when not set	None

For details on using the SLA auto-tuning feature, see the [Auto-tuning Guide](./sla_auto_tune.md).

Dataset Configuration

Parameter	Type	Description	Default
--dataset	str	Dataset mode, see Dataset Modes below	-
--dataset-path	str	Dataset file or directory path Points to a file: read directly; points to a directory: looks for the corresponding data file inside (for offline use with pre-downloaded dataset cache)	-
--data-source	str	Data source for dataset loading: modelscope, huggingface, or local Defaults to modelscope when not specified; automatically treated as local when --dataset-path is a local directory	modelscope
--dataset-args	str	Per-dataset arguments (JSON string), validated against the schema of the selected --dataset (unknown keys raise an error)	-

The keys carried by --dataset-args are documented in the sections where they apply:

Key	Purpose	Section
target_input_len / input_len_mode	Truncate real data to a fixed input length	Length Control
prefix_file / prefix_role	Long-context prefix injection for very long fixed-length inputs	Long-context Prefix Injection
speed / model_override / model_mapping / match_output_length	Replay behaviour for production traffic	Production Traffic Replay
Token-length arguments	Multi-turn datasets	Multi-turn Conversation

`--multi-turn-args` is deprecated; use `--dataset-args` instead (the key names are unchanged). The old flag still works and is automatically merged into `--dataset-args` (on a key conflict, `--dataset-args` takes precedence).

Dataset Modes

Text / Chat

Mode	Description	Supports dataset-path
openqa	Automatically downloads OpenQA from ModelScope Prompts are relatively short (usually <100 tokens) Uses question field from jsonl file when dataset_path is specified	✓
longalpaca	Automatically downloads LongAlpaca-12k from ModelScope Prompts are much longer (generally >6000 tokens) Uses instruction field from jsonl file when dataset_path is specified	✓
line_by_line	Each line in txt file is used as a separate prompt Requires dataset_path	✓ (Required)
random	Randomly generates prompts based on prefix-length, max-prompt-length, and min-prompt-length Requires tokenizer-path Usage example	✗
custom	Custom dataset parser See Custom Dataset Guide	✓

Multimodal

Mode	Description	Supports dataset-path
flickr8k	Automatically downloads Flick8k from ModelScope Builds image-text inputs; large dataset suitable for evaluating multimodal models Supports --dataset-path pointing to a local dataset directory (offline)	✓ (directory)
kontext_bench	Automatically downloads Kontext-Bench from ModelScope Builds image-text inputs; approximately 1,000 samples, suitable for quick evaluation of multimodal models Supports --dataset-path pointing to a local dataset directory (offline)	✓ (directory)
random_vl	Randomly generates both image and text inputs Based on random, with additional image-related parameters Usage example	✗

Embedding

Mode	Description	Supports dataset-path
embedding	Load text data from file to evaluate Embedding model Supports Line-by-line (TXT) or JSONL format (with text field)	✓ (Required)
random_embedding	Randomly generate queries based on max-prompt-length and min-prompt-length to evaluate Embedding model Must specify tokenizer-path	✗
embedding_batch	Batch send text data to evaluate Embedding model Load data from file Supports --extra-args '{"batch_size": 8}' to set batch size	✓ (Required)
random_embedding_batch	Batch send randomly generated query data to evaluate Embedding model Must specify tokenizer-path Supports --extra-args '{"batch_size": 8}' to set batch size	✗

Rerank

Mode	Description	Supports dataset-path
rerank	Load Query-Document pairs from file to evaluate Rerank model Supports JSONL format (with query and documents fields)	✓ (Required)
random_rerank	Randomly generate query data to evaluate Rerank model Must specify tokenizer-path Supports --extra-args '{"num_documents": 10, "document_length_ratio": 5}' to set number of documents and length ratio	✗

Multi-turn Conversation

Must be used with --multi-turn; see Multi-turn Conversation for the parameters and the Multi-turn Benchmark Guide for details.

Mode	Description	Supports dataset-path
random_multi_turn	Synthetic multi-turn conversations; each turn randomly generates a token sequence Requires --tokenizer-path and --max-turns Usage example	✗
share_gpt_zh_multi_turn	Automatically downloads the Chinese ShareGPT dataset (~70k conversations) from ModelScope, preserving full multi-turn conversations Usage example	✓
share_gpt_en_multi_turn	Automatically downloads the English ShareGPT dataset (~70k conversations) from ModelScope, preserving full multi-turn conversations	✓
custom_multi_turn	Uses a local JSONL file as a custom multi-turn dataset Each line must be a JSON array of OpenAI message dicts; ideal for benchmarking with your own conversation data Requires --dataset-path Usage example	✓ (Required)

Production Traffic Replay

Must be used with --open-loop; see Production Traffic Replay for the trace file format and replay arguments.

Mode	Description	Supports dataset-path
workload_trace	Replays a recorded production-traffic JSONL verbatim — original timestamps, request bodies, and headers — for benchmarking against real-world load (bursty arrivals, heterogeneous requests, multi-model routing) Each request carries its own model, preserving multi-model routing Requires --open-loop and --dataset-path; --model/--number are optional (the trace carries its own model and count)	✓ (Required)

Input Construction

Controls the content and length of the input sent to the model. Below, --xxx entries are command-line flags while bare keys are passed through the --dataset-args JSON.

Length Control

Parameter	Type	Description	Default
--max-prompt-length	int	Maximum input prompt length Prompts exceeding this length will be discarded	131072
--min-prompt-length	int	Minimum input prompt length Prompts shorter than this will be discarded	0

To benchmark a fixed input length with real data (instead of random), use the following --dataset-args keys. Supported on openqa, longalpaca, line_by_line (plain-text lines only), and ShareGPT (share_gpt_zh / share_gpt_en). Requires --tokenizer-path.

Key	Description	Default
target_input_len	Target input length in tokens. When set, every prompt is truncated to this length	disabled
input_len_mode	What to do with prompts shorter than the target: cap (keep as-is; that prompt may be shorter than the target); drop (discard it, so every emitted prompt is exactly the target). drop cannot be combined with prefix_file (see Long-context Prefix Injection)	cap

# Truncate every input to 2048 tokens
evalscope perf \
  --model qwen2.5 --url http://127.0.0.1:8000/v1/completions \
  --dataset share_gpt_zh --tokenizer-path /path/to/tokenizer \
  --dataset-args '{"target_input_len": 2048}'

Lengths are counted as bare content tokens, without chat-template overhead. Multi-turn datasets like ShareGPT fit/filter only the last user turn by default (same as single-turn); the whole-conversation budget (sum of all message contents, over-long dropped, short padded by the prefix) applies only when a prefix_file is configured (see Long-context Prefix Injection). JSON lines in line_by_line (messages array / full request body) do not go through length control, so combining them with these keys raises an error.

How it differs from --max/min-prompt-length:

• --max/min-prompt-length only filters and never changes content — samples outside the range are dropped, so you get real samples of varying lengths;
• target_input_len rewrites content — it truncates every prompt to the given length, ideal for controlled fixed-length benchmarking.

To get "every prompt exactly N tokens", you must use target_input_len; setting --min-prompt-length equal to --max-prompt-length cannot achieve it (real data almost never has prompts of exactly N tokens, so they get filtered out). The random dataset is the exception — it is generated on the fly, so min=max already yields a fixed length and this arg is not needed.

Long-context Prefix Injection

Real instruction datasets are mostly 4K-8K tokens, so setting target_input_len to 128K filters everything out in drop mode and leaves varying lengths in cap mode. prefix_file lets you point at a long text (e.g. a book or document corpus); the framework slices it to exactly target_input_len − prompt length tokens and prepends it to each short prompt, so every request's total input hits the target length while keeping the low-entropy character of real human language (ideal for measuring prefix-cache hit rates and MTP acceptance rates). Supported on the same datasets as Length Control.

Key	Description	Default
prefix_file	Path to the long prefix text file (UTF-8 plain text). Requires target_input_len and cannot be combined with input_len_mode="drop"	disabled
prefix_role	Injection role for the prefix: system (injected as a leading system message, matching real RAG traffic; inference engines usually have dedicated prefix-cache handling for system prompts); user (prepended directly to the user message content)	system

# Align every request to exactly 131072 tokens using a long text prefix injected as the system role
evalscope perf \
  --model qwen2.5 --url http://127.0.0.1:8000/v1/chat/completions \
  --dataset openqa --tokenizer-path /path/to/tokenizer \
  --dataset-args '{"target_input_len": 131072, "prefix_file": "/path/to/long_text.txt", "prefix_role": "system"}'

Behavior notes:

• Budget split: the prompt is kept as-is (over-length prompts are truncated per input_len_mode); the prefix is sliced to exactly target_input_len − tokens of all message contents, so the total equals the target. Multi-turn history counts towards the budget (see the length convention in Length Control).
• Incompatible with drop: drop only keeps prompts that already fill target_input_len, leaving a zero prefix budget, so the injection could never take effect — the combination is rejected at config time. Use cap plus prefix filling for fixed lengths.
• Short prefix: when the prefix file has fewer tokens than the remaining budget, it is repeated (tiled) to cover it and then truncated precisely, with a warning.
• Fallback: when apply_chat_template is off (e.g. the /v1/completions endpoint), a system message cannot be injected, so the prefix falls back to plain-text concatenation with a warning.
• Join boundary: with prefix_role="user" and in the plain-text fallback the prefix sits directly next to the prompt. The prefix and prompt are counted independently, so when the tokenizer merges or splits characters across the join the measured total can differ from the target by about ±1 token. prefix_role="system" (chat-template mode) is separated by message markers and is always exact.
• Cache friendly: all requests share the same prefix head (lengths differ slightly per prompt), which naturally suits prefix-cache hit testing.

The `prefix_file` in this section injects a **real text** prefix for real datasets, whereas `--prefix-length` injects a **random token** prefix and only applies to the `random` dataset (see [Random Data Generation](#random-data-generation) below). They serve different purposes and should not be confused.

Random Data Generation

Parameter	Type	Description	Default
--prefix-length	int	Length of the random token prefix Only effective for the random dataset; all requests share the same prefix, which can be used to induce prefix-cache hits	0
--image-width	int	Image width for random VL dataset	224
--image-height	int	Image height for random VL dataset	224
--image-format	str	Image format for random VL dataset	RGB
--image-num	int	Number of images for random VL dataset	1
--image-patch-size	int	Patch size for the image Only used for local image token calculation	28

The length of random prompts is set by --min-prompt-length / --max-prompt-length (equal values yield a fixed length); target_input_len is not needed.

Prompt and Template

Parameter	Type	Description	Default
--prompt	str	Specify request prompt String or local file (specify via @/path/to/file) Higher priority than dataset Example: @./prompt.txt	-
--query-template	str	Specify query template JSON string or local file (specify via @/path/to/file) Example: @./query_template.json	-
--apply-chat-template	bool	Whether to apply chat template	None (automatically determined based on URL suffix)
--tokenize-prompt	bool	Tokenize the prompt client-side into a token-ID list and send it directly via /v1/completions, bypassing server-side re-tokenization	False

Multi-turn Conversation

Parameter	Type	Description	Default
--multi-turn	bool	Enable multi-turn conversation benchmark mode; --number is the total number of turns to send and --parallel is the number of concurrent turn-level requests	False
--min-turns	int	Minimum number of user turns per conversation; used by random_multi_turn and swe_smith	1
--max-turns	int	Maximum number of user turns per conversation; required for random_multi_turn; optional for ShareGPT / custom_multi_turn (truncates long conversations); for swe_smith it's the upper bound for per-conversation turn sampling, falling back to --min-turns when unset	None
--num-workers	int	Worker processes for CPU-bound dataset/request generation. 0 = auto-detect from CPU affinity; 1 = serial (no multiprocessing); >1 = explicit worker count. Used by random (long-prompt parallel generation) and swe_smith (live construction). Supersedes the deprecated multi_turn_args.num_workers.	0

Token-length arguments for multi-turn datasets such as swe_smith are passed via --dataset-args.

Available multi-turn datasets are listed in [Dataset Modes](#dataset-modes); for full usage see the [Multi-turn Benchmark Guide](./multi_turn.md).

Production Traffic Replay

Use --dataset workload_trace to replay recorded production traffic verbatim following its original arrival timing, closely matching real-world load. Requires --open-loop; no --rate is needed (arrival times come from the trace timestamps). See the full example at Production Traffic Replay.

The trace file is JSONL, one request record per line:

{"body": {"model": "qwen-plus", "messages": [{"role": "user", "content": "hi"}]}, "timestamp": 1700000000.0}
{"body": {"model": "qwen-max", "messages": [{"role": "user", "content": "hello"}]}, "timestamp": 1700000001.5, "headers": {"X-Tag": "exp"}, "request_id": "req-42", "completion_tokens": 256}

Field	Required	Description
body	✓	Complete request body (dict or JSON string), sent as-is
timestamp	✓	Arrival time (number or ISO-8601 string); only relative deltas matter; must be monotonically non-decreasing
headers		Per-request HTTP headers (merged with CLI headers, CLI wins; hop-by-hop headers are stripped)
request_id		Propagated to results for correlation with the original request
completion_tokens		Used together with match_output_length

Replay behaviour is tuned via --dataset-args:

Key	Type	Description	Default
speed	float	Replay speed multiplier (2.0 = 2× faster, 0.5 = 2× slower)	1.0
model_override	str	Replace the model of every request with this value	disabled
model_mapping	dict	Remap model by name (a match takes priority; unmatched keeps the original)	disabled
match_output_length	bool	Set max_tokens from the recorded completion_tokens and enable ignore_eos (requires vLLM or compatible; ignore_eos is auto-skipped for constrained-decoding requests)	false

`--model` **does not rewrite** the trace body for `workload_trace` — each request keeps its own `model`, preserving multi-model routing. To rewrite models, use `model_override` / `model_mapping`.

Model and Generation

Parameter	Type	Description	Default
--tokenizer-path	str	Tokenizer weights path Used to calculate the number of tokens in input and output Usually located in the same directory as model weights When benchmarking a chat endpoint, the tokenizer must ship a chat template (see the note below)	None
--frequency-penalty	float	frequency_penalty value	-
--logprobs	bool	Whether to return logarithmic probabilities	-
--max-tokens	int or int int	Maximum number of tokens that can be generated • A single integer: fixed value, e.g. --max-tokens 2048 • Two integers: min max, sampled uniformly at random per request, e.g. --max-tokens 512 2048	2048
--min-tokens	int	Minimum number of tokens to generate Note: Not all model services support this parameter For vLLM>=0.8.1, you need to additionally set --extra-args '{"ignore_eos": true}' In closed-loop mode, setting this equal to --max-tokens gives every request the same duration, so they finish together and are re-released together, showing up as a TTFT ramp that repeats every --parallel requests; use the --max-tokens <min> <max> range form to avoid it, or --open-loop (arrivals are decoupled from completions)	-
--n-choices	int	Number of completion choices to generate	-
--seed	int	Random seed	None
--stop	str	Tokens that stop the generation	-
--stop-token-ids	list[int]	IDs of tokens that stop the generation	-
--temperature	float	Sampling temperature	0
--top-p	float	Top-p sampling	-
--top-k	int	Top-k sampling	-
--extra-args	str	Additional parameters to be passed in the request body JSON string format Example: '{"ignore_eos": true}'	-

Tokenizer and chat template

When benchmarking a chat/completions endpoint, --apply-chat-template is on by default and the client applies the chat template before counting tokens, so client-side lengths line up with the usage.prompt_tokens reported by the service; the tokenizer given to --tokenizer-path must therefore ship a Jinja chat template. DeepSeek-V3.2 / V4 provide encoding scripts instead, and base / pretrain checkpoints have no template either — those fail with an error that lists the available options.

Two things to watch out for: without --tokenizer-path, --min-prompt-length / --max-prompt-length filter by characters instead of tokens; and borrowing another model's tokenizer does not fail, but a mismatched vocabulary silently distorts token counts.

Output

Parameter	Type	Description	Default
--visualizer	str	Visualizer to use Options: wandb, swanlab, clearml If set, metrics will be saved to the specified visualizer	None
--enable-progress-tracker	bool	Whether to enable progress tracking, writing hierarchical stress-test progress to progress.json in real time, queryable via the service API	False
--wandb-api-key	str	wandb API key for logging metrics to wandb Deprecated, please use --visualizer wandb instead	-
--swanlab-api-key	str	swanlab API key for logging metrics to swanlab Deprecated, please use --visualizer swanlab instead	-
--outputs-dir	str	Output file path	./outputs
--no-timestamp	bool	Exclude timestamp from output directory name	False

Other Parameters

Parameter	Type	Description	Default
--db-commit-interval	int	Number of rows buffered before writing results to SQLite database	1000
--queue-size-multiplier	int	Maximum size of the request queue Calculated as: parallel * multiplier	5
--in-flight-task-multiplier	int	Maximum number of in-flight tasks Calculated as: parallel * multiplier	2