latency.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
"""Benchmark the latency of processing a single batch of requests."""

import argparse
import dataclasses
import json
import os
import time
from typing import Any

import numpy as np
from tqdm import tqdm

from vllm.benchmarks.lib.utils import convert_to_pytorch_benchmark_format, write_to_json
from vllm.engine.arg_utils import EngineArgs
from vllm.inputs import PromptType
from vllm.sampling_params import BeamSearchParams


def save_to_pytorch_benchmark_format(
    args: argparse.Namespace, results: dict[str, Any]
) -> None:
    pt_records = convert_to_pytorch_benchmark_format(
        args=args,
        metrics={"latency": results["latencies"]},
        extra_info={k: results[k] for k in ["avg_latency", "percentiles"]},
    )
    if pt_records:
        pt_file = f"{os.path.splitext(args.output_json)[0]}.pytorch.json"
        write_to_json(pt_file, pt_records)


def add_cli_args(parser: argparse.ArgumentParser):
    parser.add_argument("--input-len", type=int, default=32)
    parser.add_argument("--output-len", type=int, default=128)
    parser.add_argument("--batch-size", type=int, default=8)
    parser.add_argument(
        "--n",
        type=int,
        default=1,
        help="Number of generated sequences per prompt.",
    )
    parser.add_argument("--use-beam-search", action="store_true")
    parser.add_argument(
        "--num-iters-warmup",
        type=int,
        default=10,
        help="Number of iterations to run for warmup.",
    )
    parser.add_argument(
        "--num-iters", type=int, default=30, help="Number of iterations to run."
    )
    parser.add_argument(
        "--profile",
        action="store_true",
        help="profile the generation process of a single batch",
    )
    parser.add_argument(
        "--output-json",
        type=str,
        default=None,
        help="Path to save the latency results in JSON format.",
    )
    parser.add_argument(
        "--disable-detokenize",
        action="store_true",
        help=(
            "Do not detokenize responses (i.e. do not include "
            "detokenization time in the latency measurement)"
        ),
    )

    parser = EngineArgs.add_cli_args(parser)
    # V1 enables prefix caching by default which skews the latency
    # numbers. We need to disable prefix caching by default.
    parser.set_defaults(enable_prefix_caching=False)


def main(args: argparse.Namespace):
    engine_args = EngineArgs.from_cli_args(args)
    if args.profile and not engine_args.profiler_config.profiler == "torch":
        raise ValueError(
            "The torch profiler is not enabled. Please provide profiler_config."
        )

    # Lazy import to avoid importing LLM when the bench command is not selected.
    from vllm import LLM, SamplingParams

    # NOTE(woosuk): If the request cannot be processed in a single batch,
    # the engine will automatically process the request in multiple batches.
    llm = LLM(**dataclasses.asdict(engine_args))
    assert llm.llm_engine.model_config.max_model_len >= (
        args.input_len + args.output_len
    ), (
        "Please ensure that max_model_len is greater than"
        " the sum of input_len and output_len."
    )

    sampling_params = SamplingParams(
        n=args.n,
        temperature=1.0,
        top_p=1.0,
        ignore_eos=True,
        max_tokens=args.output_len,
        detokenize=not args.disable_detokenize,
    )
    dummy_prompt_token_ids = np.random.randint(
        10000, size=(args.batch_size, args.input_len)
    )
    dummy_prompts: list[PromptType] = [
        {"prompt_token_ids": batch} for batch in dummy_prompt_token_ids.tolist()
    ]

    def llm_generate():
        if not args.use_beam_search:
            llm.generate(dummy_prompts, sampling_params=sampling_params, use_tqdm=False)
        else:
            llm.beam_search(
                dummy_prompts,
                BeamSearchParams(
                    beam_width=args.n,
                    max_tokens=args.output_len,
                    ignore_eos=True,
                ),
            )

    def run_to_completion(profile_dir: str | None = None):
        if profile_dir:
            llm.start_profile()
            llm_generate()
            llm.stop_profile()
        else:
            start_time = time.perf_counter()
            llm_generate()
            end_time = time.perf_counter()
            latency = end_time - start_time
            return latency

    print("Warming up...")
    for _ in tqdm(range(args.num_iters_warmup), desc="Warmup iterations"):
        run_to_completion(profile_dir=None)

    if args.profile:
        profile_dir = engine_args.profiler_config.torch_profiler_dir
        print(f"Profiling (results will be saved to '{profile_dir}')...")
        run_to_completion(profile_dir=profile_dir)
        return

    # Benchmark.
    latencies = []
    for _ in tqdm(range(args.num_iters), desc="Profiling iterations"):
        latencies.append(run_to_completion(profile_dir=None))
    latencies = np.array(latencies)
    percentages = [10, 25, 50, 75, 90, 99]
    percentiles = np.percentile(latencies, percentages)
    print(f"Avg latency: {np.mean(latencies)} seconds")
    for percentage, percentile in zip(percentages, percentiles):
        print(f"{percentage}% percentile latency: {percentile} seconds")

    # Output JSON results if specified
    if args.output_json:
        results = {
            "avg_latency": np.mean(latencies),
            "latencies": latencies.tolist(),
            "percentiles": dict(zip(percentages, percentiles.tolist())),
        }
        with open(args.output_json, "w") as f:
            json.dump(results, f, indent=4)
        save_to_pytorch_benchmark_format(args, results)