[Misc][Benchmarking] Add variable request-rate ("ramp-up") to the benchmarking client. (#19423)

Signed-off-by: dtransposed <damian@damian-ml-machine.europe-west3-b.c.jetbrains-grazie.internal>
Co-authored-by: dtransposed <damian@damian-ml-machine.europe-west3-b.c.jetbrains-grazie.internal>
Co-authored-by: Roger Wang <hey@rogerw.me>

Author: 3 people

benchmarks/README.md

@@ -269,6 +269,21 @@ python3 vllm/benchmarks/benchmark_serving.py \
   --num-prompts 10
 ```
 
+### Running With Ramp-Up Request Rate
+
+The benchmark tool also supports ramping up the request rate over the
+duration of the benchmark run. This can be useful for stress testing the
+server or finding the maximum throughput that it can handle, given some latency budget.
+
+Two ramp-up strategies are supported:
+- `linear`: Increases the request rate linearly from a start value to an end value.
+- `exponential`: Increases the request rate exponentially.
+
+The following arguments can be used to control the ramp-up:
+- `--ramp-up-strategy`: The ramp-up strategy to use (`linear` or `exponential`).
+- `--ramp-up-start-rps`: The request rate at the beginning of the benchmark.
+- `--ramp-up-end-rps`: The request rate at the end of the benchmark.
+
 ---
 ## Example - Offline Throughput Benchmark
 

benchmarks/benchmark_serving.py

@@ -33,7 +33,7 @@
 from collections.abc import AsyncGenerator, Iterable
 from dataclasses import dataclass
 from datetime import datetime
-from typing import Any, Optional
+from typing import Any, Literal, Optional
 
 import numpy as np
 from tqdm.asyncio import tqdm
@@ -107,14 +107,42 @@ class BenchmarkMetrics:
     percentiles_e2el_ms: list[tuple[float, float]]
 
 
+def _get_current_request_rate(
+    ramp_up_strategy: Optional[Literal["linear", "exponential"]],
+    ramp_up_start_rps: Optional[int],
+    ramp_up_end_rps: Optional[int],
+    request_index: int,
+    total_requests: int,
+    request_rate: float,
+) -> float:
+    if (
+        ramp_up_strategy
+        and ramp_up_start_rps is not None
+        and ramp_up_end_rps is not None
+    ):
+        progress = request_index / max(total_requests - 1, 1)
+        if ramp_up_strategy == "linear":
+            increase = (ramp_up_end_rps - ramp_up_start_rps) * progress
+            return ramp_up_start_rps + increase
+        elif ramp_up_strategy == "exponential":
+            ratio = ramp_up_end_rps / ramp_up_start_rps
+            return ramp_up_start_rps * (ratio**progress)
+        else:
+            raise ValueError(f"Unknown ramp-up strategy: {ramp_up_strategy}")
+    return request_rate
+
+
 async def get_request(
     input_requests: list[SampleRequest],
     request_rate: float,
     burstiness: float = 1.0,
-) -> AsyncGenerator[SampleRequest, None]:
+    ramp_up_strategy: Optional[Literal["linear", "exponential"]] = None,
+    ramp_up_start_rps: Optional[int] = None,
+    ramp_up_end_rps: Optional[int] = None,
+) -> AsyncGenerator[tuple[SampleRequest, float], None]:
     """
     Asynchronously generates requests at a specified rate
-    with OPTIONAL burstiness.
+    with OPTIONAL burstiness and OPTIONAL ramp-up strategy.
 
     Args:
         input_requests:
@@ -129,22 +157,44 @@ async def get_request(
             A lower burstiness value (0 < burstiness < 1) results
             in more bursty requests, while a higher burstiness value
             (burstiness > 1) results in a more uniform arrival of requests.
+         ramp_up_strategy (optional):
+            The ramp-up strategy. Can be "linear" or "exponential".
+            If None, uses constant request rate (specified by request_rate).
+        ramp_up_start_rps (optional):
+            The starting request rate for ramp-up.
+        ramp_up_end_rps (optional):
+            The ending request rate for ramp-up.
     """
-    input_requests: Iterable[SampleRequest] = iter(input_requests)
-
-    # Calculate scale parameter theta to maintain the desired request_rate.
     assert burstiness > 0, (
         f"A positive burstiness factor is expected, but given {burstiness}."
     )
-    theta = 1.0 / (request_rate * burstiness)
+    # Convert to list to get length for ramp-up calculations
+    if isinstance(input_requests, Iterable) and not isinstance(input_requests, list):
+        input_requests = list(input_requests)
+
+    total_requests = len(input_requests)
+    request_index = 0
 
     for request in input_requests:
-        yield request
+        current_request_rate = _get_current_request_rate(
+            ramp_up_strategy,
+            ramp_up_start_rps,
+            ramp_up_end_rps,
+            request_index,
+            total_requests,
+            request_rate,
+        )
+
+        yield request, current_request_rate
 
-        if request_rate == float("inf"):
+        request_index += 1
+
+        if current_request_rate == float("inf"):
             # If the request rate is infinity, then we don't need to wait.
             continue
 
+        theta = 1.0 / (current_request_rate * burstiness)
+
         # Sample the request interval from the gamma distribution.
         # If burstiness is 1, it follows exponential distribution.
         interval = np.random.gamma(shape=burstiness, scale=theta)
@@ -290,6 +340,9 @@ async def benchmark(
     max_concurrency: Optional[int],
     lora_modules: Optional[Iterable[str]],
     extra_body: Optional[dict],
+    ramp_up_strategy: Optional[Literal["linear", "exponential"]] = None,
+    ramp_up_start_rps: Optional[int] = None,
+    ramp_up_end_rps: Optional[int] = None,
 ):
     if backend in ASYNC_REQUEST_FUNCS:
         request_func = ASYNC_REQUEST_FUNCS[backend]
@@ -353,7 +406,15 @@ async def benchmark(
 
     distribution = "Poisson process" if burstiness == 1.0 else "Gamma distribution"
 
-    print(f"Traffic request rate: {request_rate}")
+    if ramp_up_strategy is not None:
+        print(
+            f"Traffic ramp-up strategy: {ramp_up_strategy}. Will increase "
+            f"RPS from {ramp_up_start_rps} to {ramp_up_end_rps} RPS over "
+            "the duration of the benchmark."
+        )
+    else:
+        print(f"Traffic request rate: {request_rate} RPS.")
+
     print(f"Burstiness factor: {burstiness} ({distribution})")
     print(f"Maximum request concurrency: {max_concurrency}")
 
@@ -373,7 +434,34 @@ async def limited_request_func(request_func_input, pbar):
 
     benchmark_start_time = time.perf_counter()
     tasks: list[asyncio.Task] = []
-    async for request in get_request(input_requests, request_rate, burstiness):
+
+    rps_change_events = []
+    last_int_rps = -1
+    if ramp_up_strategy is not None and ramp_up_start_rps is not None:
+        last_int_rps = ramp_up_start_rps
+        rps_change_events.append(
+            {
+                "rps": last_int_rps,
+                "timestamp": datetime.now().isoformat(),
+            }
+        )
+
+    async for request, current_request_rate in get_request(
+        input_requests,
+        request_rate,
+        burstiness,
+        ramp_up_strategy,
+        ramp_up_start_rps,
+        ramp_up_end_rps,
+    ):
+        if ramp_up_strategy is not None:
+            current_int_rps = int(current_request_rate)
+            if current_int_rps > last_int_rps:
+                timestamp = datetime.now().isoformat()
+                for rps_val in range(last_int_rps + 1, current_int_rps + 1):
+                    rps_change_events.append({"rps": rps_val, "timestamp": timestamp})
+                last_int_rps = current_int_rps
+
         prompt, prompt_len, output_len, mm_content = (
             request.prompt,
             request.prompt_len,
@@ -397,11 +485,8 @@ async def limited_request_func(request_func_input, pbar):
             ignore_eos=ignore_eos,
             extra_body=extra_body,
         )
-        tasks.append(
-            asyncio.create_task(
-                limited_request_func(request_func_input=request_func_input, pbar=pbar)
-            )
-        )
+        task = limited_request_func(request_func_input=request_func_input, pbar=pbar)
+        tasks.append(asyncio.create_task(task))
     outputs: list[RequestFuncOutput] = await asyncio.gather(*tasks)
 
     if profile:
@@ -477,6 +562,9 @@ async def limited_request_func(request_func_input, pbar):
         "errors": [output.error for output in outputs],
     }
 
+    if rps_change_events:
+        result["rps_change_events"] = rps_change_events
+
     def process_one_metric(
         # E.g., "ttft"
         metric_attribute_name: str,
@@ -610,6 +698,26 @@ def main(args: argparse.Namespace):
     tokenizer_id = args.tokenizer if args.tokenizer is not None else args.model
     tokenizer_mode = args.tokenizer_mode
 
+    # Validate ramp-up arguments
+    if args.ramp_up_strategy is not None:
+        if args.request_rate != float("inf"):
+            raise ValueError(
+                "When using ramp-up, do not specify --request-rate. "
+                "The request rate will be controlled by ramp-up parameters. "
+                "Please remove the --request-rate argument."
+            )
+        if args.ramp_up_start_rps is None or args.ramp_up_end_rps is None:
+            raise ValueError(
+                "When using --ramp-up-strategy, both --ramp-up-start-rps and "
+                "--ramp-up-end-rps must be specified"
+            )
+        if args.ramp_up_start_rps < 0 or args.ramp_up_end_rps < 0:
+            raise ValueError("Ramp-up start and end RPS must be non-negative")
+        if args.ramp_up_start_rps > args.ramp_up_end_rps:
+            raise ValueError("Ramp-up start RPS must be less than end RPS")
+        if args.ramp_up_strategy == "exponential" and args.ramp_up_start_rps == 0:
+            raise ValueError("For exponential ramp-up, the start RPS cannot be 0.")
+
     if args.base_url is not None:
         api_url = f"{args.base_url}{args.endpoint}"
         base_url = f"{args.base_url}"
@@ -802,6 +910,9 @@ def main(args: argparse.Namespace):
             max_concurrency=args.max_concurrency,
             lora_modules=args.lora_modules,
             extra_body=sampling_params,
+            ramp_up_strategy=args.ramp_up_strategy,
+            ramp_up_start_rps=args.ramp_up_start_rps,
+            ramp_up_end_rps=args.ramp_up_end_rps,
         )
     )
 
@@ -834,6 +945,11 @@ def main(args: argparse.Namespace):
         result_json["burstiness"] = args.burstiness
         result_json["max_concurrency"] = args.max_concurrency
 
+        if args.ramp_up_strategy is not None:
+            result_json["ramp_up_strategy"] = args.ramp_up_strategy
+            result_json["ramp_up_start_rps"] = args.ramp_up_start_rps
+            result_json["ramp_up_end_rps"] = args.ramp_up_end_rps
+
         # Merge with benchmark result
         result_json = {**result_json, **benchmark_result}
 
@@ -859,7 +975,10 @@ def main(args: argparse.Namespace):
             if args.max_concurrency is not None
             else ""
         )
-        file_name = f"{backend}-{args.request_rate}qps{max_concurrency_str}-{base_model_id}-{current_dt}.json"  # noqa
+        if args.ramp_up_strategy is not None:
+            file_name = f"{backend}-ramp-up-{args.ramp_up_strategy}-{args.ramp_up_start_rps}qps-{args.ramp_up_end_rps}qps{max_concurrency_str}-{base_model_id}-{current_dt}.json"  # noqa
+        else:
+            file_name = f"{backend}-{args.request_rate}qps{max_concurrency_str}-{base_model_id}-{current_dt}.json"  # noqa
         if args.result_filename:
             file_name = args.result_filename
         if args.result_dir:
@@ -1225,6 +1344,31 @@ def create_argument_parser():
         "script chooses a LoRA module at random.",
     )
 
+    parser.add_argument(
+        "--ramp-up-strategy",
+        type=str,
+        default=None,
+        choices=["linear", "exponential"],
+        help="The ramp-up strategy. This would be used to "
+        "ramp up the request rate from initial RPS to final "
+        "RPS rate (specified by --ramp-up-start-rps and --ramp-up-end-rps). "
+        "over the duration of the benchmark.",
+    )
+    parser.add_argument(
+        "--ramp-up-start-rps",
+        type=int,
+        default=None,
+        help="The starting request rate for ramp-up (RPS). "
+        "Needs to be specified when --ramp-up-strategy is used.",
+    )
+    parser.add_argument(
+        "--ramp-up-end-rps",
+        type=int,
+        default=None,
+        help="The ending request rate for ramp-up (RPS). "
+        "Needs to be specified when --ramp-up-strategy is used.",
+    )
+
     return parser