Fix log_every_n_steps check in ThroughputMonitor

[awaelchli]

What does this PR do?

Fixes #19461

The ThroughputMonitor has a check for whether accumulate_grad_batches divides log_every_n_steps. But since logging only happens when the optimizer steps (at the end of accumulation), the error checking is not needed and incorrect. This PR removes the check.

Example:

import os

import torch
from lightning.pytorch import LightningModule, Trainer
from torch.utils.data import DataLoader, Dataset
from lightning.pytorch.callbacks import ThroughputMonitor


class RandomDataset(Dataset):
    def __init__(self, size, length):
        self.len = length
        self.data = torch.randn(length, size)

    def __getitem__(self, index):
        return self.data[index]

    def __len__(self):
        return self.len


class BoringModel(LightningModule):
    def __init__(self):
        super().__init__()
        self.layer = torch.nn.Linear(32, 2)

    def forward(self, x):
        return self.layer(x)

    def training_step(self, batch, batch_idx):
        loss = self(batch).sum()
        self.log("train_loss", loss)
        return {"loss": loss}

    def validation_step(self, batch, batch_idx):
        loss = self(batch).sum()
        self.log("valid_loss", loss)

    def configure_optimizers(self):
        return torch.optim.SGD(self.layer.parameters(), lr=0.1)


train_data = DataLoader(RandomDataset(32, 64), batch_size=2)
val_data = DataLoader(RandomDataset(32, 64), batch_size=2)

model = BoringModel()
trainer = Trainer(
    callbacks=ThroughputMonitor(batch_size_fn=lambda batch: batch.size(0)),
    default_root_dir=os.getcwd(),
    max_epochs=2,
    log_every_n_steps=2,
    accumulate_grad_batches=5,
    enable_model_summary=False,
)
trainer.fit(model, train_dataloaders=train_data, val_dataloaders=val_data)

---

📚 Documentation preview 📚: https://pytorch-lightning--19470.org.readthedocs.build/en/19470/

cc @Borda @carmocca

[github-actions]

⚡ Required checks status: All passing 🟢

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🟢 pytorch_lightning: Tests workflow

Check ID	Status
pl-cpu (macOS-11, lightning, 3.8, 1.13, oldest)	success	✅
pl-cpu (macOS-11, lightning, 3.10, 1.13)	success	✅
pl-cpu (macOS-11, lightning, 3.10, 2.1)	success	✅
pl-cpu (macOS-11, lightning, 3.10, 2.2)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.8, 1.13, oldest)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.10, 1.13)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.10, 2.1)	success	✅
pl-cpu (ubuntu-20.04, lightning, 3.10, 2.2)	success	✅
pl-cpu (windows-2022, lightning, 3.8, 1.13, oldest)	success	✅
pl-cpu (windows-2022, lightning, 3.10, 1.13)	success	✅
pl-cpu (windows-2022, lightning, 3.10, 2.1)	success	✅
pl-cpu (windows-2022, lightning, 3.10, 2.2)	success	✅
pl-cpu (macOS-11, pytorch, 3.8, 1.13)	success	✅
pl-cpu (ubuntu-20.04, pytorch, 3.8, 1.13)	success	✅
pl-cpu (windows-2022, pytorch, 3.8, 1.13)	success	✅
pl-cpu (macOS-12, pytorch, 3.11, 2.0)	success	✅
pl-cpu (macOS-12, pytorch, 3.11, 2.1)	success	✅
pl-cpu (ubuntu-22.04, pytorch, 3.11, 2.0)	success	✅
pl-cpu (ubuntu-22.04, pytorch, 3.11, 2.1)	success	✅
pl-cpu (windows-2022, pytorch, 3.11, 2.0)	success	✅
pl-cpu (windows-2022, pytorch, 3.11, 2.1)	success	✅

These checks are required after the changes to src/lightning/pytorch/callbacks/throughput_monitor.py, tests/tests_pytorch/callbacks/test_throughput_monitor.py.

🟢 pytorch_lightning: Azure GPU

Check ID	Status
pytorch-lightning (GPUs) (testing Lightning | latest)	success	✅
pytorch-lightning (GPUs) (testing PyTorch | latest)	success	✅

These checks are required after the changes to src/lightning/pytorch/callbacks/throughput_monitor.py, tests/tests_pytorch/callbacks/test_throughput_monitor.py.

🟢 pytorch_lightning: Benchmarks

Check ID	Status
lightning.Benchmarks	success	✅

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🟢 pytorch_lightning: Docs

Check ID	Status
docs-make (pytorch, doctest)	success	✅
docs-make (pytorch, html)	success	✅

These checks are required after the changes to src/lightning/pytorch/callbacks/throughput_monitor.py.

🟢 mypy

Check ID	Status
mypy	success	✅

These checks are required after the changes to src/lightning/pytorch/callbacks/throughput_monitor.py.

🟢 install

Check ID	Status
install-pkg (ubuntu-22.04, app, 3.8)	success	✅
install-pkg (ubuntu-22.04, app, 3.11)	success	✅
install-pkg (ubuntu-22.04, fabric, 3.8)	success	✅
install-pkg (ubuntu-22.04, fabric, 3.11)	success	✅
install-pkg (ubuntu-22.04, pytorch, 3.8)	success	✅
install-pkg (ubuntu-22.04, pytorch, 3.11)	success	✅
install-pkg (ubuntu-22.04, lightning, 3.8)	success	✅
install-pkg (ubuntu-22.04, lightning, 3.11)	success	✅
install-pkg (ubuntu-22.04, notset, 3.8)	success	✅
install-pkg (ubuntu-22.04, notset, 3.11)	success	✅
install-pkg (macOS-12, app, 3.8)	success	✅
install-pkg (macOS-12, app, 3.11)	success	✅
install-pkg (macOS-12, fabric, 3.8)	success	✅
install-pkg (macOS-12, fabric, 3.11)	success	✅
install-pkg (macOS-12, pytorch, 3.8)	success	✅
install-pkg (macOS-12, pytorch, 3.11)	success	✅
install-pkg (macOS-12, lightning, 3.8)	success	✅
install-pkg (macOS-12, lightning, 3.11)	success	✅
install-pkg (macOS-12, notset, 3.8)	success	✅
install-pkg (macOS-12, notset, 3.11)	success	✅
install-pkg (windows-2022, app, 3.8)	success	✅
install-pkg (windows-2022, app, 3.11)	success	✅
install-pkg (windows-2022, fabric, 3.8)	success	✅
install-pkg (windows-2022, fabric, 3.11)	success	✅
install-pkg (windows-2022, pytorch, 3.8)	success	✅
install-pkg (windows-2022, pytorch, 3.11)	success	✅
install-pkg (windows-2022, lightning, 3.8)	success	✅
install-pkg (windows-2022, lightning, 3.11)	success	✅
install-pkg (windows-2022, notset, 3.8)	success	✅
install-pkg (windows-2022, notset, 3.11)	success	✅

These checks are required after the changes to src/lightning/pytorch/callbacks/throughput_monitor.py.

---

Thank you for your contribution! 💜

Note
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[codecov]

Codecov Report

Merging #19470 (42af40e) into master (d61f6fe) will decrease coverage by 35%.
Report is 10 commits behind head on master.
The diff coverage is 100%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #19470      +/-   ##
==========================================
- Coverage      84%      48%     -35%     
==========================================
  Files         450      442       -8     
  Lines       38091    37970     -121     
==========================================
- Hits        31814    18373   -13441     
- Misses       6277    19597   +13320     

[carmocca]

Thank you!