Fix warmup steps calculation when gradient_accumulation is used

src/refiners/training_utils/trainer.py

@@ -102,18 +102,18 @@ def scoped_seed(seed: int | Callable[..., int] | None = None) -> Callable[..., C
 class WarmupScheduler(LRScheduler):
     _step_count: int  # defined by LRScheduler
 
-    def __init__(self, optimizer: Optimizer, scheduler: LRScheduler, warmup_steps: int = 0) -> None:
+    def __init__(self, optimizer: Optimizer, scheduler: LRScheduler, warmup_scheduler_steps: int = 0) -> None:
-        self.warmup_steps = warmup_steps
+        self.warmup_scheduler_steps = warmup_scheduler_steps
         self.scheduler = scheduler
         super().__init__(optimizer=optimizer)
 
     def get_lr(self) -> list[float] | float:  # type: ignore
-        if self._step_count < self.warmup_steps:
+        if self._step_count <= self.warmup_scheduler_steps:
-            return [base_lr * self._step_count / self.warmup_steps for base_lr in self.base_lrs]
+            return [base_lr * self._step_count / self.warmup_scheduler_steps for base_lr in self.base_lrs]
         return self.scheduler.get_lr()
 
     def step(self, epoch: int | None = None) -> None:
-        if self._step_count < self.warmup_steps:
+        if self._step_count < self.warmup_scheduler_steps:
             super().step()
         else:
             self.scheduler.step(epoch=epoch)
@@ -342,19 +342,19 @@ class Trainer(Generic[ConfigType, Batch], ABC):
     @cached_property
     def lr_scheduler(self) -> LRScheduler:
         config = self.config.scheduler
-        step_size = self.clock.convert_time_unit_to_steps(
+        scheduler_step_size = config.update_interval["number"]
-            number=config.update_interval["number"], unit=config.update_interval["unit"]
-        )
 
         match config.scheduler_type:
             case SchedulerType.CONSTANT_LR:
                 lr_scheduler = LambdaLR(optimizer=self.optimizer, lr_lambda=lambda _: 1.0)
             case SchedulerType.STEP_LR:
-                lr_scheduler = StepLR(optimizer=self.optimizer, step_size=step_size, gamma=config.gamma)
+                lr_scheduler = StepLR(optimizer=self.optimizer, step_size=scheduler_step_size, gamma=config.gamma)
             case SchedulerType.EXPONENTIAL_LR:
                 lr_scheduler = ExponentialLR(optimizer=self.optimizer, gamma=config.gamma)
             case SchedulerType.COSINE_ANNEALING_LR:
-                lr_scheduler = CosineAnnealingLR(optimizer=self.optimizer, T_max=step_size, eta_min=config.eta_min)
+                lr_scheduler = CosineAnnealingLR(
+                    optimizer=self.optimizer, T_max=scheduler_step_size, eta_min=config.eta_min
+                )
             case SchedulerType.REDUCE_LR_ON_PLATEAU:
                 lr_scheduler = cast(
                     LRScheduler,
@@ -372,12 +372,14 @@ class Trainer(Generic[ConfigType, Batch], ABC):
                 assert config.lr_lambda is not None, "lr_lambda must be specified to use LambdaLR"
                 lr_scheduler = LambdaLR(optimizer=self.optimizer, lr_lambda=config.lr_lambda)
             case SchedulerType.ONE_CYCLE_LR:
-                lr_scheduler = OneCycleLR(optimizer=self.optimizer, max_lr=config.max_lr, total_steps=step_size)
+                lr_scheduler = OneCycleLR(
+                    optimizer=self.optimizer, max_lr=config.max_lr, total_steps=scheduler_step_size
+                )
             case SchedulerType.MULTIPLICATIVE_LR:
                 assert config.lr_lambda is not None, "lr_lambda must be specified to use MultiplicativeLR"
                 lr_scheduler = MultiplicativeLR(optimizer=self.optimizer, lr_lambda=config.lr_lambda)
             case SchedulerType.COSINE_ANNEALING_WARM_RESTARTS:
-                lr_scheduler = CosineAnnealingWarmRestarts(optimizer=self.optimizer, T_0=step_size)
+                lr_scheduler = CosineAnnealingWarmRestarts(optimizer=self.optimizer, T_0=scheduler_step_size)
             case SchedulerType.CYCLIC_LR:
                 lr_scheduler = CyclicLR(optimizer=self.optimizer, base_lr=config.base_lr, max_lr=config.max_lr)
             case SchedulerType.MULTI_STEP_LR:
@@ -385,12 +387,12 @@ class Trainer(Generic[ConfigType, Batch], ABC):
             case _:
                 raise ValueError(f"Unknown scheduler type: {config.scheduler_type}")
 
-        warmup_steps = self.clock.convert_time_unit_to_steps(number=config.warmup["number"], unit=config.warmup["unit"])
+        warmup_scheduler_steps = self.clock.convert_time_value(config.warmup, config.update_interval["unit"])
-        if warmup_steps > 0:
+        if warmup_scheduler_steps > 0:
             lr_scheduler = WarmupScheduler(
                 optimizer=self.optimizer,
                 scheduler=lr_scheduler,
-                warmup_steps=warmup_steps,
+                warmup_scheduler_steps=warmup_scheduler_steps,
             )
 
         return lr_scheduler

tests/training_utils/test_trainer.py

@@ -6,6 +6,7 @@ from warnings import warn
 import pytest
 import torch
 from torch import Tensor, nn
+from torch.optim import SGD
 from torch.utils.data import Dataset
 
 from refiners.fluxion import layers as fl
@@ -14,6 +15,7 @@ from refiners.training_utils.config import BaseConfig, TimeUnit
 from refiners.training_utils.trainer import (
     Trainer,
     TrainingClock,
+    WarmupScheduler,
     count_learnable_parameters,
     human_readable_number,
 )
@@ -183,3 +185,24 @@ def test_training_cycle(mock_trainer: MockTrainer) -> None:
     assert clock.step == config.training.duration["number"] * clock.num_batches_per_epoch
 
     assert mock_trainer.step_counter == mock_trainer.clock.step
+
+
+@pytest.fixture
+def warmup_scheduler():
+    optimizer = SGD([nn.Parameter(torch.randn(2, 2), requires_grad=True)], lr=0.1)
+    scheduler = torch.optim.lr_scheduler.ConstantLR(optimizer, 1)
+    return WarmupScheduler(optimizer, scheduler, warmup_scheduler_steps=100)
+
+
+def test_initial_lr(warmup_scheduler: WarmupScheduler) -> None:
+    optimizer = warmup_scheduler.optimizer
+    for group in optimizer.param_groups:
+        assert group["lr"] == 1e-3
+
+
+def test_warmup_lr(warmup_scheduler: WarmupScheduler) -> None:
+    for _ in range(102):
+        warmup_scheduler.step()
+    optimizer = warmup_scheduler.optimizer
+    for group in optimizer.param_groups:
+        assert group["lr"] == 0.1