Configurable LR schedulers (#604)

* Initial config handler and test

* Added means to run from CLI

* Update lora config loading and tests

* Constrain scheduler config (warmup and minimum LR) for each kind

* Update reference to moved schedule_config module

* Minor fix

* Fix typos

* Moved build_schedule and tests

* nits in schedule config

* flake

* fix path

---------

Co-authored-by: Awni Hannun <awni@apple.com>

llms/mlx_lm/examples/lora_config.yaml

@@ -16,7 +16,7 @@ lora_layers: 16
 batch_size: 4
 
 # Iterations to train for.
-iters: 100
+iters: 1000
 
 # Number of validation batches, -1 uses the entire validation set.
 val_batches: 25
@@ -43,7 +43,7 @@ save_every: 100
 test: false
 
 # Number of test set batches, -1 uses the entire test set.
-test_batches: 500
+test_batches: 100
 
 # Maximum sequence length.
 max_seq_length: 2048
@@ -60,3 +60,10 @@ lora_parameters:
   alpha: 16.0
   scale: 10.0
   dropout: 0.0
+
+# Schedule can only be specified in a config file, uncomment to use.
+#lr_schedule:
+#  name: cosine_decay
+#  warmup: 100 # 0 for no warmup
+#  warmup_init: 1e-7 # 0 if not specified
+#  arguments: [1e-5, 1000, 1e-7] # passed to scheduler

llms/mlx_lm/lora.py

@@ -15,7 +15,7 @@ from mlx.utils import tree_flatten
 
 from .tuner.datasets import load_dataset
 from .tuner.trainer import TrainingArgs, TrainingCallback, evaluate, train
-from .tuner.utils import linear_to_lora_layers
+from .tuner.utils import build_schedule, linear_to_lora_layers
 from .utils import load
 
 yaml_loader = yaml.SafeLoader
@@ -53,6 +53,7 @@ CONFIG_DEFAULTS = {
     "test": False,
     "test_batches": 500,
     "max_seq_length": 2048,
+    "lr_schedule": None,
     "lora_parameters": {"rank": 8, "alpha": 16, "dropout": 0.0, "scale": 10.0},
 }
 
@@ -199,7 +200,13 @@ def run(args, training_callback: TrainingCallback = None):
         )
 
         model.train()
-        opt = optim.Adam(learning_rate=args.learning_rate)
+        opt = optim.Adam(
+            learning_rate=(
+                build_schedule(args.lr_schedule)
+                if args.lr_schedule
+                else args.learning_rate
+            )
+        )
         # Train model
         train(
             model=model,

llms/mlx_lm/models/gemma.py

@@ -1,6 +1,5 @@
 from dataclasses import dataclass
-from functools import partial
-from typing import Dict, Optional, Tuple, Union
+from typing import Optional, Tuple
 
 import mlx.core as mx
 import mlx.nn as nn

llms/mlx_lm/models/olmo.py

@@ -1,6 +1,6 @@
 from dataclasses import dataclass
 from sys import exit
-from typing import Dict, Optional, Tuple, Union
+from typing import Optional, Tuple
 
 import mlx.core as mx
 import mlx.nn as nn

llms/mlx_lm/models/plamo.py

@@ -1,5 +1,5 @@
 from dataclasses import dataclass
-from typing import Any, Dict, List, Optional, Tuple, Union
+from typing import Any, List, Optional, Tuple, Union
 
 import mlx.core as mx
 import mlx.nn as nn
@@ -183,11 +183,7 @@ class PlamoModel(nn.Module):
             mask = mask.astype(self.embed_tokens.weight.dtype)
 
         if cache is None:
-            past_key_values_length = 0
             cache = [None for _ in range(len(self.layers.layers))]
-        else:
-            if cache[0] is not None:
-                past_key_values_length = cache[0][0].shape[2]
 
         for e, layer in enumerate(self.layers.layers):
             h, c = layer(h, mask, cache[e])

llms/mlx_lm/tuner/utils.py

@@ -3,11 +3,32 @@ from typing import Dict
 
 import mlx.core as mx
 import mlx.nn as nn
+import mlx.optimizers as opt
 from mlx.utils import tree_unflatten
 
 from .lora import LoRALinear
 
 
+def build_schedule(schedule_config: Dict):
+    """
+    Build a learning rate schedule from the given config.
+    """
+    schedule_fn = getattr(opt.schedulers, schedule_config["name"])
+    arguments = schedule_config["arguments"]
+    initial_lr = arguments[0]
+    bound_schedule_fn = schedule_fn(*arguments)
+    if warmup_steps := schedule_config.get("warmup", 0):
+        warmup_init = schedule_config.get("warmup_init", 0.0)
+        warmup_fn = opt.schedulers.linear_schedule(
+            warmup_init, initial_lr, warmup_steps
+        )
+        return opt.schedulers.join_schedules(
+            [warmup_fn, bound_schedule_fn], [warmup_steps + 1]
+        )
+    else:
+        return bound_schedule_fn
+
+
 def linear_to_lora_layers(
     model: nn.Module,
     num_lora_layers: int,

llms/tests/test_lora.py

@@ -1,14 +1,18 @@
 # Copyright © 2024 Apple Inc.
 
+import math
 import sys
 import unittest
 from io import StringIO
 from unittest.mock import MagicMock
 
 import mlx.nn as nn
+import mlx.optimizers as opt
 from mlx.utils import tree_flatten
 from mlx_lm import lora, tuner
+from mlx_lm.lora import yaml_loader
 from mlx_lm.tuner.lora import LoRALinear
+from mlx_lm.tuner.utils import build_schedule
 
 
 class TestLora(unittest.TestCase):
@@ -120,5 +124,52 @@ class TestLora(unittest.TestCase):
         self.assertEqual(self.capturedOutput.getvalue(), expected_output)
 
 
+class TestScheduleConfig(unittest.TestCase):
+    def test_join(self):
+        config = {"name": "cosine_decay", "warmup": 100, "arguments": [1e-5, 100]}
+        cos_with_warmup = build_schedule(config)
+        self.assertIsNotNone(cos_with_warmup)
+
+        self.assertEqual(cos_with_warmup(0), 0.0)
+        self.assertAlmostEqual(cos_with_warmup(101), 1e-5, delta=1e-1)
+        optimizer = opt.Adam(learning_rate=cos_with_warmup)
+        for _ in range(100):
+            optimizer.update({}, {})
+        self.assertAlmostEqual(optimizer.learning_rate.item(), 1e-5, delta=1e-1)
+        for _ in range(100):
+            optimizer.update({}, {})
+        expected_lr = 1e-5 * 0.5 * (1.0 + math.cos(math.pi * 200 / 10))
+        self.assertAlmostEqual(optimizer.learning_rate.item(), expected_lr, delta=1e-1)
+
+    def test_single_schedule(self):
+
+        config = {
+            "name": "cosine_decay",
+            "arguments": [0.1, 10],
+        }
+        lr_schedule = build_schedule(config)
+        lr = lr_schedule(4)
+        expected_lr = 0.1 * 0.5 * (1.0 + math.cos(math.pi * 4 / 10))
+        self.assertAlmostEqual(lr, expected_lr, delta=1e-7)
+
+    def test_non_zero_warmup(self):
+        config = {
+            "name": "cosine_decay",
+            "warmup": 10,
+            "warmup_init": 1e-6,
+            "arguments": [1e-5, 20],
+        }
+        lr_schedule = build_schedule(config)
+        lr = lr_schedule(0)
+        self.assertAlmostEqual(lr, 1e-6, delta=1e-7)
+
+    def test_malformed_config(self):
+        config = {"warmup": 100}
+        self.assertRaises(KeyError, build_schedule, config)
+
+        config = {"cosine_decay": None}
+        self.assertRaises(KeyError, build_schedule, config)
+
+
 if __name__ == "__main__":
     unittest.main()