#!/usr/bin/env python3 -u
# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.
"""
Evaluate the perplexity of a trained language model.
"""
import logging
import math
import os
import sys
from argparse import Namespace
from typing import Iterable, List, Optional
import torch
import fairseq
from fairseq import checkpoint_utils, distributed_utils, options, tasks, utils
from fairseq.dataclass.utils import convert_namespace_to_omegaconf
from fairseq.logging import progress_bar
from fairseq.logging.meters import StopwatchMeter
from fairseq.sequence_scorer import SequenceScorer
from omegaconf import DictConfig
logging.basicConfig(
format="%(asctime)s | %(levelname)s | %(name)s | %(message)s",
datefmt="%Y-%m-%d %H:%M:%S",
level=os.environ.get("LOGLEVEL", "INFO").upper(),
stream=sys.stdout,
)
logger = logging.getLogger("fairseq_cli.eval_lm")
def eval_lm(
models: List[fairseq.models.FairseqModel],
source_dictionary: fairseq.data.Dictionary,
batch_iterator: Iterable,
post_process: Optional[str] = None,
output_word_probs: bool = False,
output_word_stats: bool = False,
target_dictionary: Optional[fairseq.data.Dictionary] = None,
softmax_batch: int = 0,
remove_bos_token: bool = False,
device: Optional[torch.device] = None,
):
"""
Args:
models (List[~fairseq.models.FairseqModel]): list of models to
evaluate. Models are essentially `nn.Module` instances, but
must be compatible with fairseq's `SequenceScorer`.
source_dictionary (~fairseq.data.Dictionary): dictionary for
applying any relevant post processing or outputing word
probs/stats.
batch_iterator (Iterable): yield batches of data
post_process (Optional[str]): post-process text by removing BPE,
letter segmentation, etc. Valid options can be found in
fairseq.data.utils.post_process, although not all options
are implemented here.
output_word_probs (Optional[bool]): output words and their
predicted log probabilities
output_word_stats (Optional[bool]): output word statistics such
as word count and average probability
target_dictionary (Optional[~fairseq.data.Dictionary]): output
dictionary (defaults to *source_dictionary*)
softmax_batch (Optional[bool]): if BxT is more than this, will
batch the softmax over vocab to this amount of tokens, in
order to fit into GPU memory
remove_bos_token (Optional[bool]): if True, confirm that the
first token is the beginning-of-sentence symbol (according
to the relevant dictionary) and remove it from the output
device (Optional[torch.device]): device to use for evaluation
(defaults to device of first model parameter)
"""
if target_dictionary is None:
target_dictionary = source_dictionary
if device is None:
device = next(models[0].parameters()).device
gen_timer = StopwatchMeter()
scorer = SequenceScorer(target_dictionary, softmax_batch)
score_sum = 0.0
count = 0
if post_process is not None:
if post_process in {"subword_nmt", "@@ "}:
bpe_cont = post_process.rstrip()
bpe_toks = {
i
for i in range(len(source_dictionary))
if source_dictionary[i].endswith(bpe_cont)
}
else:
raise NotImplementedError(
"--post-process={post_process} is not implemented"
)
bpe_len = len(bpe_cont)
else:
bpe_toks = None
bpe_len = 0
word_stats = dict()
for sample in batch_iterator:
if "net_input" not in sample:
continue
sample = utils.move_to_cuda(sample, device=device)
gen_timer.start()
hypos = scorer.generate(models, sample)
gen_timer.stop(sample["ntokens"])
for i, hypos_i in enumerate(hypos):
hypo = hypos_i[0]
sample_id = sample["id"][i]
tokens = hypo["tokens"]
tgt_len = tokens.numel()
pos_scores = hypo["positional_scores"].float()
if remove_bos_token:
assert hypo["tokens"][0].item() == target_dictionary.bos()
tokens = tokens[1:]
pos_scores = pos_scores[1:]
skipped_toks = 0
if bpe_toks is not None:
for i in range(tgt_len - 1):
if tokens[i].item() in bpe_toks:
skipped_toks += 1
pos_scores[i + 1] += pos_scores[i]
pos_scores[i] = 0
inf_scores = pos_scores.eq(float("inf")) | pos_scores.eq(float("-inf"))
if inf_scores.any():
logger.info(
"skipping tokens with inf scores:",
target_dictionary.string(tokens[inf_scores.nonzero()]),
)
pos_scores = pos_scores[(~inf_scores).nonzero()]
score_sum += pos_scores.sum().cpu()
count += pos_scores.numel() - skipped_toks
if output_word_probs or output_word_stats:
w = ""
word_prob = []
is_bpe = False
for i in range(len(tokens)):
w_ind = tokens[i].item()
w += source_dictionary[w_ind]
if bpe_toks is not None and w_ind in bpe_toks:
w = w[:-bpe_len]
is_bpe = True
else:
word_prob.append((w, pos_scores[i].item()))
next_prob = None
ind = i + 1
while ind < len(tokens):
if pos_scores[ind].item() != 0:
next_prob = pos_scores[ind]
break
ind += 1
word_stats.setdefault(w, WordStat(w, is_bpe)).add(
pos_scores[i].item(), next_prob
)
is_bpe = False
w = ""
if output_word_probs:
logger.info(
str(int(sample_id))
+ " "
+ (
"\t".join(
"{} [{:2f}]".format(x[0], x[1]) for x in word_prob
)
)
)
avg_nll_loss = (
-score_sum / count / math.log(2) if count > 0 else 0
) # convert to base 2
logger.info(
"Evaluated {:,} tokens in {:.1f}s ({:.2f} tokens/s)".format(
gen_timer.n, gen_timer.sum, 1.0 / gen_timer.avg if gen_timer.avg > 0 else 0
)
)
if output_word_stats:
for ws in sorted(word_stats.values(), key=lambda x: x.count, reverse=True):
logger.info(ws)
return {
"loss": avg_nll_loss,
"perplexity": 2 ** avg_nll_loss,
}
class WordStat(object):
def __init__(self, word, is_bpe):
self.word = word
self.is_bpe = is_bpe
self.log_prob = 0
self.next_word_prob = 0
self.count = 0
self.missing_next_words = 0
def add(self, log_prob, next_word_prob):
"""increments counters for the sum of log probs of current word and next
word (given context ending at current word). Since the next word might be at the end of the example,
or it might be not counted because it is not an ending subword unit,
also keeps track of how many of those we have seen"""
if next_word_prob is not None:
self.next_word_prob += next_word_prob
else:
self.missing_next_words += 1
self.log_prob += log_prob
self.count += 1
def __str__(self):
return "{}\t{}\t{}\t{}\t{}\t{}".format(
self.word,
self.count,
self.log_prob,
self.is_bpe,
self.next_word_prob,
self.count - self.missing_next_words,
)
def main(cfg: DictConfig, **unused_kwargs):
if isinstance(cfg, Namespace):
cfg = convert_namespace_to_omegaconf(cfg)
utils.import_user_module(cfg.common)
logger.info(cfg)
if cfg.eval_lm.context_window > 0:
# reduce tokens per sample by the required context window size
cfg.task.tokens_per_sample -= cfg.eval_lm.context_window
# Initialize the task using the current *cfg*
task = tasks.setup_task(cfg.task)
# Load ensemble
logger.info("loading model(s) from {}".format(cfg.common_eval.path))
models, model_args, task = checkpoint_utils.load_model_ensemble_and_task(
[cfg.common_eval.path],
arg_overrides=eval(cfg.common_eval.model_overrides),
suffix=cfg.checkpoint.checkpoint_suffix,
strict=(cfg.checkpoint.checkpoint_shard_count == 1),
num_shards=cfg.checkpoint.checkpoint_shard_count,
task=task,
)
use_fp16 = cfg.common.fp16
use_cuda = torch.cuda.is_available() and not cfg.common.cpu
if use_cuda:
torch.cuda.set_device(cfg.distributed_training.device_id)
# Optimize ensemble for generation and set the source and dest dicts on the model
# (required by scorer)
for model in models:
if use_fp16:
model.half()
if use_cuda and not cfg.distributed_training.pipeline_model_parallel:
model.cuda()
model.prepare_for_inference_(cfg)
assert len(models) > 0
logger.info(
"num. model params: {:,}".format(sum(p.numel() for p in models[0].parameters()))
)
# Load dataset splits
task.load_dataset(cfg.dataset.gen_subset)
dataset = task.dataset(cfg.dataset.gen_subset)
logger.info(
"{} {} {:,} examples".format(
cfg.task.data, cfg.dataset.gen_subset, len(dataset)
)
)
itr = task.eval_lm_dataloader(
dataset=dataset,
max_tokens=cfg.dataset.max_tokens or 36000,
batch_size=cfg.dataset.batch_size,
max_positions=utils.resolve_max_positions(
*[model.max_positions() for model in models]
),
num_shards=max(
cfg.dataset.num_shards,
cfg.distributed_training.distributed_world_size,
),
shard_id=max(
cfg.dataset.shard_id,
cfg.distributed_training.distributed_rank,
),
num_workers=cfg.dataset.num_workers,
data_buffer_size=cfg.dataset.data_buffer_size,
context_window=cfg.eval_lm.context_window,
)
itr = progress_bar.progress_bar(
itr,
log_format=cfg.common.log_format,
log_interval=cfg.common.log_interval,
default_log_format=("tqdm" if not cfg.common.no_progress_bar else "simple"),
)
results = eval_lm(
models=models,
source_dictionary=task.source_dictionary,
batch_iterator=itr,
post_process=cfg.common_eval.post_process,
output_word_probs=cfg.eval_lm.output_word_probs,
output_word_stats=cfg.eval_lm.output_word_stats,
target_dictionary=task.target_dictionary,
softmax_batch=cfg.eval_lm.softmax_batch,
remove_bos_token=getattr(cfg.task, "add_bos_token", False),
)
logger.info(
"Loss (base 2): {:.4f}, Perplexity: {:.2f}".format(
results["loss"], results["perplexity"]
)
)
return results
def cli_main():
parser = options.get_eval_lm_parser()
args = options.parse_args_and_arch(parser)
distributed_utils.call_main(convert_namespace_to_omegaconf(args), main)
if __name__ == "__main__":
cli_main()