[Feature] Support reduce_lr_update

mmcv/runner/hooks/lr_updater.py

@@ -1,6 +1,7 @@
 # Copyright (c) Open-MMLab. All rights reserved.
 import numbers
 from math import cos, pi
+from typing import Optional
 
 import mmcv
 from .hook import HOOKS, Hook
@@ -614,3 +615,223 @@ def format_param(name, optim, param):
         if name not in param:
             raise KeyError(f'{name} is not found in {param.keys()}')
         return param[name]
+
+
+@HOOKS.register_module()
+class ReduceLrUpdateHook(LrUpdaterHook):
+    """ReduceLROnPlateau Scheduler.
+
+    Reduce learning rate when a metric has stopped improving. This scheduler
+    reads a metrics quantity and if no improvement is seen for a 'patience'
+    number of epochs, the learning rate is reduced.
+
+    Args:
+        periods (list[int]): Periods that taking the metric value in count.
+        val_metric (str, optional): Metrics to be evaluated. If val_metric is
+            None, the metrics will be loss value. Default: None.
+        mode (str, optional): One of `min`, `max`. In `min` mode, lr will
+            be reduced when the quantity monitored has stopped
+            decreasing; in `max` mode it will be reduced when the
+            quantity monitored has stopped increasing. Default: 'min'.
+        factor (float, optional): Factor by which the learning rate will be
+            reduced. new_lr = lr * factor. Default: 0.1.
+        patience (int, optional): Number of epochs with no improvement after
+            which learning rate will be reduced. For example, if
+            `patience = 2`, then we will ignore the first 2 epochs
+            with no improvement, and will only decrease the LR after the
+            3rd epoch if the loss still hasn't improved then.
+            Default: 10.
+        threshold (float, optional): Threshold for measuring the new optimum,
+            to only focus on significant changes. Default: 1e-4.
+        threshold_mode (str, optional): One of `rel`, `abs`. In `rel` mode,
+            dynamic_threshold = best * ( 1 + threshold ) in 'max'
+            mode or best * ( 1 - threshold ) in `min` mode.
+            In `abs` mode, dynamic_threshold = best + threshold in
+            `max` mode or best - threshold in `min` mode. Default: 'rel'.
+        cooldown (int, optional): Number of epochs to wait before resuming
+            normal operation after lr has been reduced. Default: 0.
+        min_lr (float, optional): Minimum LR value to keep. If LR after decay
+            is lower than `min_lr`, it will be clipped to this value.
+            Default: 0.
+        eps (float, optional): Minimal decay applied to lr. If the difference
+            between new and old lr is smaller than eps, the update is
+            ignored. Default: 1e-8.
+    """
+
+    def __init__(self,
+                 periods: list,
+                 val_metric: Optional[str] = None,
+                 mode: str = 'min',
+                 factor: float = 0.1,
+                 patience: int = 10,
+                 threshold: float = 1e-4,
+                 threshold_mode: str = 'rel',
+                 cooldown: int = 0,
+                 min_lr: float = 0.,
+                 eps: float = 1e-8,
+                 **kwargs):
+        assert isinstance(periods, list), '"periods" must be a list'
+        assert mmcv.is_list_of(periods, int) and all([s >= 0 for s in periods])
+        self.periods = periods
+        self.val_metric = val_metric
+
+        if mode not in ['min', 'max']:
+            raise ValueError(
+                'mode must be one of "min" or "max", instead got {mode}')
+        self.mode = mode
+
+        if factor >= 1.0:
+            raise ValueError('Factor should be < 1.0')
+        self.factor = factor
+
+        self.patience = patience
+        self.threshold = threshold
+
+        if threshold_mode not in ['rel', 'abs']:
+            raise ValueError('thresh_mode must be one of "rel" or "abs",\
+                 instead got {threshold_mode}')
+        self.threshold_mode = threshold_mode
+
+        self.cooldown = cooldown
+        self.cooldown_counter = 0
+        self.best = None
+        self.num_bad_epochs = None
+        self.mode_worse = None  # the worse value for the chosen mode
+        self.min_lr = min_lr
+        self.eps = eps
+        self.last_epoch = 0
+        self._init_is_better(self.mode)
+        self._reset()
+        super(ReduceLrUpdateHook, self).__init__(**kwargs)
+
+    def get_lr(self, runner, regular_lr):
+        if self.num_bad_epochs > self.patience:
+            self.cooldown_counter = self.cooldown
+            self.num_bad_epochs = 0
+            if regular_lr - regular_lr * self.factor > self.eps:
+                new_lr = max(regular_lr * self.factor, self.min_lr)
+            else:
+                new_lr = regular_lr
+            return new_lr
+        else:
+            return regular_lr
+
+    def get_regular_lr(self, runner):
+        if not self.regular_lr:
+            self.regular_lr = self.base_lr
+        if isinstance(runner.optimizer, dict):
+            lr_groups = {}
+            for k in runner.optimizer.keys():
+                _lr_group = [
+                    self.get_lr(runner, _regular_lr)
+                    for _regular_lr in self.regular_lr[k]
+                ]
+                lr_groups.update({k: _lr_group})
+            return lr_groups
+        else:
+            return [
+                self.get_lr(runner, _regular_lr)
+                for _regular_lr in self.regular_lr
+            ]
+
+    def _init_is_better(self, mode):
+        if mode == 'min':
+            self.mode_worse = float('inf')
+        else:
+            self.mode_worse = float('-inf')
+
+    def _reset(self):
+        self.best = self.mode_worse
+        self.cooldown_counter = 0
+        self.num_bad_epochs = 0
+
+    def is_better(self, a, best):
+        if self.mode == 'min' and self.threshold_mode == 'rel':
+            rel_epsilon = 1. - self.threshold
+            return a < best * rel_epsilon
+        elif self.mode == 'min' and self.threshold_mode == 'abs':
+            return a < best - self.threshold
+        elif self.mode == 'max' and self.threshold_mode == 'rel':
+            rel_epsilon = 1. + self.threshold
+            return a > best * rel_epsilon
+        else:
+            return a > best + self.threshold
+
+    @property
+    def in_cooldown(self):
+        return self.cooldown_counter > 0
+
+    def after_train_epoch(self, runner):
+        if not self.by_epoch:
+            return
+        cur_epoch = runner.epoch
+        if self.warmup is not None and self.warmup_by_epoch:
+            if cur_epoch <= self.warmup_epochs:
+                return
+        if cur_epoch in self.periods and self.val_metric is None:
+            current = runner.outputs['loss']
+            if self.is_better(current, self.best):
+                self.best = current
+                self.num_bad_epochs = 0
+            else:
+                self.num_bad_epochs += 1
+
+            if self.in_cooldown:
+                self.cooldown_counter -= 1
+                self.num_bad_epochs = 0
+        print('epoch--', cur_epoch, ' lr:', self.regular_lr)
+
+    def after_train_iter(self, runner):
+        if self.by_epoch:
+            return
+        cur_iter = runner.iter
+        if self.warmup_epochs is not None and cur_iter <= self.warmup_iters:
+            return
+        if cur_iter in self.periods and self.val_metric is None:
+            current = runner.outputs['loss']
+            if self.is_better(current, self.best):
+                self.best = current
+                self.num_bad_epochs = 0
+            else:
+                self.num_bad_epochs += 1
+
+            if self.in_cooldown:
+                self.cooldown_counter -= 1
+                self.num_bad_epochs = 0
+
+    def after_val_epoch(self, runner):
+        if not self.by_epoch:
+            return
+        cur_epoch = runner.epoch
+        if self.warmup is not None and self.warmup_by_epoch:
+            if cur_epoch <= self.warmup_epochs:
+                return
+        if cur_epoch in self.periods and self.val_metric is not None:
+            current = runner.outputs[self.val_metric]
+            if self.is_better(current, self.best):
+                self.best = current
+                self.num_bad_epochs = 0
+            else:
+                self.num_bad_epochs += 1
+
+            if self.in_cooldown:
+                self.cooldown_counter -= 1
+                self.num_bad_epochs = 0
+
+    def after_val_iter(self, runner):
+        if self.by_epoch:
+            return
+        cur_iter = runner.iter
+        if self.warmup_epochs is not None and cur_iter <= self.warmup_iters:
+            return
+        if cur_iter in self.periods and self.val_metric is not None:
+            current = runner.outputs[self.val_metric]
+            if self.is_better(current, self.best):
+                self.best = current
+                self.num_bad_epochs = 0
+            else:
+                self.num_bad_epochs += 1
+
+            if self.in_cooldown:
+                self.cooldown_counter -= 1
+                self.num_bad_epochs = 0