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| # Copyright (c) Facebook, Inc. and its affiliates. | |
| import logging | |
| import numpy as np | |
| from itertools import count | |
| from typing import List, Tuple | |
| import torch | |
| import tqdm | |
| from fvcore.common.timer import Timer | |
| from detectron2.utils import comm | |
| from .build import build_batch_data_loader | |
| from .common import DatasetFromList, MapDataset | |
| from .samplers import TrainingSampler | |
| logger = logging.getLogger(__name__) | |
| class _EmptyMapDataset(torch.utils.data.Dataset): | |
| """ | |
| Map anything to emptiness. | |
| """ | |
| def __init__(self, dataset): | |
| self.ds = dataset | |
| def __len__(self): | |
| return len(self.ds) | |
| def __getitem__(self, idx): | |
| _ = self.ds[idx] | |
| return [0] | |
| def iter_benchmark( | |
| iterator, num_iter: int, warmup: int = 5, max_time_seconds: float = 60 | |
| ) -> Tuple[float, List[float]]: | |
| """ | |
| Benchmark an iterator/iterable for `num_iter` iterations with an extra | |
| `warmup` iterations of warmup. | |
| End early if `max_time_seconds` time is spent on iterations. | |
| Returns: | |
| float: average time (seconds) per iteration | |
| list[float]: time spent on each iteration. Sometimes useful for further analysis. | |
| """ | |
| num_iter, warmup = int(num_iter), int(warmup) | |
| iterator = iter(iterator) | |
| for _ in range(warmup): | |
| next(iterator) | |
| timer = Timer() | |
| all_times = [] | |
| for curr_iter in tqdm.trange(num_iter): | |
| start = timer.seconds() | |
| if start > max_time_seconds: | |
| num_iter = curr_iter | |
| break | |
| next(iterator) | |
| all_times.append(timer.seconds() - start) | |
| avg = timer.seconds() / num_iter | |
| return avg, all_times | |
| class DataLoaderBenchmark: | |
| """ | |
| Some common benchmarks that help understand perf bottleneck of a standard dataloader | |
| made of dataset, mapper and sampler. | |
| """ | |
| def __init__( | |
| self, | |
| dataset, | |
| *, | |
| mapper, | |
| sampler=None, | |
| total_batch_size, | |
| num_workers=0, | |
| max_time_seconds: int = 90, | |
| ): | |
| """ | |
| Args: | |
| max_time_seconds (int): maximum time to spent for each benchmark | |
| other args: same as in `build.py:build_detection_train_loader` | |
| """ | |
| if isinstance(dataset, list): | |
| dataset = DatasetFromList(dataset, copy=False, serialize=True) | |
| if sampler is None: | |
| sampler = TrainingSampler(len(dataset)) | |
| self.dataset = dataset | |
| self.mapper = mapper | |
| self.sampler = sampler | |
| self.total_batch_size = total_batch_size | |
| self.num_workers = num_workers | |
| self.per_gpu_batch_size = self.total_batch_size // comm.get_world_size() | |
| self.max_time_seconds = max_time_seconds | |
| def _benchmark(self, iterator, num_iter, warmup, msg=None): | |
| avg, all_times = iter_benchmark(iterator, num_iter, warmup, self.max_time_seconds) | |
| if msg is not None: | |
| self._log_time(msg, avg, all_times) | |
| return avg, all_times | |
| def _log_time(self, msg, avg, all_times, distributed=False): | |
| percentiles = [np.percentile(all_times, k, interpolation="nearest") for k in [1, 5, 95, 99]] | |
| if not distributed: | |
| logger.info( | |
| f"{msg}: avg={1.0/avg:.1f} it/s, " | |
| f"p1={percentiles[0]:.2g}s, p5={percentiles[1]:.2g}s, " | |
| f"p95={percentiles[2]:.2g}s, p99={percentiles[3]:.2g}s." | |
| ) | |
| return | |
| avg_per_gpu = comm.all_gather(avg) | |
| percentiles_per_gpu = comm.all_gather(percentiles) | |
| if comm.get_rank() > 0: | |
| return | |
| for idx, avg, percentiles in zip(count(), avg_per_gpu, percentiles_per_gpu): | |
| logger.info( | |
| f"GPU{idx} {msg}: avg={1.0/avg:.1f} it/s, " | |
| f"p1={percentiles[0]:.2g}s, p5={percentiles[1]:.2g}s, " | |
| f"p95={percentiles[2]:.2g}s, p99={percentiles[3]:.2g}s." | |
| ) | |
| def benchmark_dataset(self, num_iter, warmup=5): | |
| """ | |
| Benchmark the speed of taking raw samples from the dataset. | |
| """ | |
| def loader(): | |
| while True: | |
| for k in self.sampler: | |
| yield self.dataset[k] | |
| self._benchmark(loader(), num_iter, warmup, "Dataset Alone") | |
| def benchmark_mapper(self, num_iter, warmup=5): | |
| """ | |
| Benchmark the speed of taking raw samples from the dataset and map | |
| them in a single process. | |
| """ | |
| def loader(): | |
| while True: | |
| for k in self.sampler: | |
| yield self.mapper(self.dataset[k]) | |
| self._benchmark(loader(), num_iter, warmup, "Single Process Mapper (sec/sample)") | |
| def benchmark_workers(self, num_iter, warmup=10): | |
| """ | |
| Benchmark the dataloader by tuning num_workers to [0, 1, self.num_workers]. | |
| """ | |
| candidates = [0, 1] | |
| if self.num_workers not in candidates: | |
| candidates.append(self.num_workers) | |
| dataset = MapDataset(self.dataset, self.mapper) | |
| for n in candidates: | |
| loader = build_batch_data_loader( | |
| dataset, | |
| self.sampler, | |
| self.total_batch_size, | |
| num_workers=n, | |
| ) | |
| self._benchmark( | |
| iter(loader), | |
| num_iter * max(n, 1), | |
| warmup * max(n, 1), | |
| f"DataLoader ({n} workers, bs={self.per_gpu_batch_size})", | |
| ) | |
| del loader | |
| def benchmark_IPC(self, num_iter, warmup=10): | |
| """ | |
| Benchmark the dataloader where each worker outputs nothing. This | |
| eliminates the IPC overhead compared to the regular dataloader. | |
| PyTorch multiprocessing's IPC only optimizes for torch tensors. | |
| Large numpy arrays or other data structure may incur large IPC overhead. | |
| """ | |
| n = self.num_workers | |
| dataset = _EmptyMapDataset(MapDataset(self.dataset, self.mapper)) | |
| loader = build_batch_data_loader( | |
| dataset, self.sampler, self.total_batch_size, num_workers=n | |
| ) | |
| self._benchmark( | |
| iter(loader), | |
| num_iter * max(n, 1), | |
| warmup * max(n, 1), | |
| f"DataLoader ({n} workers, bs={self.per_gpu_batch_size}) w/o comm", | |
| ) | |
| def benchmark_distributed(self, num_iter, warmup=10): | |
| """ | |
| Benchmark the dataloader in each distributed worker, and log results of | |
| all workers. This helps understand the final performance as well as | |
| the variances among workers. | |
| It also prints startup time (first iter) of the dataloader. | |
| """ | |
| gpu = comm.get_world_size() | |
| dataset = MapDataset(self.dataset, self.mapper) | |
| n = self.num_workers | |
| loader = build_batch_data_loader( | |
| dataset, self.sampler, self.total_batch_size, num_workers=n | |
| ) | |
| timer = Timer() | |
| loader = iter(loader) | |
| next(loader) | |
| startup_time = timer.seconds() | |
| logger.info("Dataloader startup time: {:.2f} seconds".format(startup_time)) | |
| comm.synchronize() | |
| avg, all_times = self._benchmark(loader, num_iter * max(n, 1), warmup * max(n, 1)) | |
| del loader | |
| self._log_time( | |
| f"DataLoader ({gpu} GPUs x {n} workers, total bs={self.total_batch_size})", | |
| avg, | |
| all_times, | |
| True, | |
| ) | |