patch to convert LR from tensor to float when using DS (axolotl-ai-cloud#2595) [skip ci]

Author: winglian

src/axolotl/core/trainer_builder.py

@@ -60,6 +60,7 @@
 from axolotl.integrations.base import PluginManager
 from axolotl.monkeypatch.multipack import SUPPORTED_MULTIPACK_MODEL_TYPES
 from axolotl.monkeypatch.relora import ReLoRACallback
+from axolotl.monkeypatch.trainer.lr import patch_trainer_get_lr
 from axolotl.processing_strategies import get_processing_strategy
 from axolotl.utils import is_comet_available, is_mlflow_available
 from axolotl.utils.callbacks import (
@@ -114,6 +115,8 @@ def __init__(self, cfg, model, tokenizer, processor=None):
         if hasattr(model, "add_model_tags"):
             model.add_model_tags(["axolotl"])
 
+        patch_trainer_get_lr()
+
     @property
     def model_ref(self):
         return self._model_ref

src/axolotl/monkeypatch/trainer/lr.py

@@ -0,0 +1,42 @@
+"""
+monkeypatch for Trainer _get_learning_rate method
+"""
+
+import logging
+
+import torch
+
+LOG = logging.getLogger(__name__)
+
+
+# TODO remove this patch once https://github.com/huggingface/transformers/pull/37881 is included in a release
+def _get_learning_rate(self):
+    if self.is_deepspeed_enabled:
+        # with deepspeed's fp16 and dynamic loss scale enabled the optimizer/scheduler steps may
+        # not run for the first few dozen steps while loss scale is too large, and thus during
+        # that time `get_last_lr` will fail if called during that warm up stage, so work around it:
+        try:
+            last_lr = self.lr_scheduler.get_last_lr()[0]
+        except AssertionError as e:
+            if "need to call step" in str(e):
+                LOG.warning(
+                    "tried to get lr value before scheduler/optimizer started stepping, returning lr=0"
+                )
+                last_lr = 0
+            else:
+                raise
+    else:
+        if isinstance(self.lr_scheduler, torch.optim.lr_scheduler.ReduceLROnPlateau):
+            last_lr = self.optimizer.param_groups[0]["lr"]
+        else:
+            last_lr = self.lr_scheduler.get_last_lr()[0]
+
+    if torch.is_tensor(last_lr):
+        last_lr = last_lr.item()
+    return last_lr
+
+
+def patch_trainer_get_lr():
+    from transformers.trainer import Trainer
+
+    Trainer._get_learning_rate = _get_learning_rate  # pylint: disable=protected-access