Multipack padding fix (#19)

For non-dolomite models, packing_max_batch_len was being calculated incorrectly. This calculates the necessary increase to make sure that average batch size is similar to the specified effective_batch_size.

---------

Signed-off-by: Mustafa Eyceoz <meyceoz@redhat.com>

src/instructlab/training/main_ds.py

@@ -461,6 +461,10 @@ def main(args):
         avg_sample_len=dataset.get_lengths().mean(),
         effective_batch_size=args.effective_batch_size,
         max_batch_len_per_gpu=args.max_batch_len,
+        is_padding=not args.is_granite,
+        dataset=dataset,
+        pad_id=tokenizer.pad_token_id,
+        seed=args.seed,
     )
     args.samples_per_gpu = (
         args.effective_batch_size // grad_accum // torch.distributed.get_world_size()

src/instructlab/training/multipack_sampler.py

@@ -25,16 +25,156 @@
 
 # Standard
 from typing import List, Optional
+import os
 
 # Third Party
-from torch.utils.data import Sampler
+from torch.utils.data import DataLoader, Sampler
 import numba
 import numpy as np
 import torch.distributed as dist
 
+# First Party
+from instructlab.training.utils import make_collate_fn
+
+
+def guess_starting_avg_padding(base_avg, goal, num_gpus, grad_accum, sorted_lengths):
+    """
+    Return a starting middle point for the binary search
+    (to find optimal addition to packing_max_batch_len
+    to account for padding)
+
+    Uses the largest initial bucket to approximate an
+    upper-bound for average padding, should overshoot.
+    """
+    addition = 0
+    packing_max_batch_len = int(
+        (base_avg + addition) * ((goal / num_gpus) / grad_accum)
+    )
+
+    bucket_zero = []
+    max = sorted_lengths[0]
+    sum = 0
+    for length in sorted_lengths:
+        if sum + max <= packing_max_batch_len:
+            sum += max
+            bucket_zero.append(length)
+        else:
+            break
+
+    total_pad = 0
+    for length in bucket_zero:
+        total_pad += max - length
+    addition = round(total_pad / len(bucket_zero))
+    return addition
+
+
+def simulate_buckets(
+    base_avg,
+    goal,
+    num_gpus,
+    grad_accum,
+    pad_id,
+    max_batch_len,
+    lengths,
+    seed,
+    dataset,
+    addition,
+):
+    """
+    Given an addition to packing_max_batch_len, simulate the
+    packing to find the updated average effective batch size.
+    """
+    packing_max_batch_len = int(
+        (base_avg + addition) * ((goal / num_gpus) / grad_accum)
+    )
+
+    collate_fn = make_collate_fn(pad_id, is_granite=False, max_batch_len=max_batch_len)
+    rank = int(os.environ["RANK"])
+    world_size = int(os.environ["WORLD_SIZE"])
+
+    sampler = MultipackDistributedBatchSampler(
+        batch_max_length=packing_max_batch_len,
+        lengths=lengths,
+        num_replicas=world_size,
+        rank=rank,
+        seed=seed,
+        padding=True,
+    )
+    simulation_loader = DataLoader(
+        dataset,
+        batch_sampler=sampler,
+        num_workers=8,
+        collate_fn=collate_fn,
+    )
+
+    avg_ebs = len(dataset) / len(simulation_loader)
+    return avg_ebs
+
+
+def find_padding_max_batch_len_addition(
+    base_avg, goal, dataset, num_gpus, grad_accum, pad_id, max_batch_len, seed
+):
+    """
+    Do a modified binary search to find optimal padding addition for
+    packing_maximum_batch_len. Starts with an upper-bound guess, and
+    increases upper-bound until guess overshoots. Then perform standard
+    binary search until within a threshold for average effective batch
+    size.
+    """
+    lengths = dataset.get_lengths()
+    sorted_lengths = list(lengths)
+    sorted_lengths.sort(reverse=True)
+
+    # Use first default bucket avg padding as starting value for addition
+    addition = guess_starting_avg_padding(
+        base_avg, goal, num_gpus, grad_accum, sorted_lengths
+    )
+
+    # binary search correct addition value from starting value
+    first_over_hit = False
+    l = 0
+    r = 2 * addition
+    while r - l > 1:
+        avg_ebs = simulate_buckets(
+            base_avg,
+            goal,
+            num_gpus,
+            grad_accum,
+            pad_id,
+            max_batch_len,
+            lengths,
+            seed,
+            dataset,
+            addition,
+        )
+
+        # check if simulation resulted in batch sizes close enough to goal and adjust if needed
+        if abs(avg_ebs - goal) <= max(10, round(goal * 0.02)):
+            break
+
+        if avg_ebs > goal:
+            first_over_hit = True
+            r = addition
+        elif avg_ebs < goal:
+            if not first_over_hit:
+                # If the starting midpoint failed to overshoot, increase the bounds of the search
+                r = r * 2
+            else:
+                l = addition
+        addition = l + ((r - l) // 2)
+
+    return addition
+
 
 def find_packing_max_batch_len_and_grad_accum(
-    num_gpus, avg_sample_len, effective_batch_size, max_batch_len_per_gpu
+    num_gpus,
+    avg_sample_len,
+    effective_batch_size,
+    max_batch_len_per_gpu,
+    is_padding,
+    dataset,
+    pad_id,
+    seed,
 ):
     """
     Calculate the minimum gradient accumulation steps required and the corresponding maximum batch length.
@@ -58,12 +198,27 @@ def find_packing_max_batch_len_and_grad_accum(
       without exceeding the per-GPU limit, and the second element is the minimum number of gradient
       accumulation steps required to maintain the effective batch size.
     """
+
     packing_max_batch_len = max_batch_len_per_gpu + 1
     grad_accum = 0
     while packing_max_batch_len > max_batch_len_per_gpu:
         grad_accum += 1
-        total_micro_batch = effective_batch_size / grad_accum
-        packing_max_batch_len = int(avg_sample_len * total_micro_batch / num_gpus)
+        total_micro_batch = (effective_batch_size / grad_accum) / num_gpus
+        if is_padding:
+            addition = find_padding_max_batch_len_addition(
+                avg_sample_len,
+                effective_batch_size,
+                dataset,
+                num_gpus,
+                grad_accum,
+                pad_id,
+                max_batch_len_per_gpu,
+                seed,
+            )
+        else:
+            addition = 0
+        packing_max_batch_len = int((avg_sample_len + addition) * total_micro_batch)
+
     return packing_max_batch_len, grad_accum
 
 

src/instructlab/training/token_dataset.py

@@ -6,11 +6,10 @@
 from torch.utils.data import DataLoader, Dataset
 import numpy as np
 import torch
-import torch.nn.functional as F
 
 # First Party
 from instructlab.training.multipack_sampler import MultipackDistributedBatchSampler
-from instructlab.training.utils import log_rank_0
+from instructlab.training.utils import log_rank_0, make_collate_fn
 
 
 class TokenDataset(Dataset):
@@ -66,94 +65,6 @@ def get_lengths(self):
         return np.array([len(self.input_ids[0])] * len(self.input_ids))
 
 
-def make_collate_fn(pad_token_id, is_granite=False, max_batch_len=60000):
-    rank = int(os.environ["RANK"])
-    if is_granite:
-
-        def pad_collate_fn(batch):
-            lens = np.array([len(item["input_ids"]) for item in batch])
-
-            cumsum_lens = np.cumsum(lens)
-            valid_up_to = int((cumsum_lens < max_batch_len).sum())
-            total_len = cumsum_lens[valid_up_to - 1]
-
-            batch = batch[:valid_up_to]
-            input_ids = [x["input_ids"].tolist() for x in batch]
-            labels = [x["labels"].tolist() for x in batch]
-            num_loss_counted_tokens = sum(
-                [(x["labels"] != -100).sum().item() for x in batch]
-            )
-
-            print(
-                f"\033[96m total length: {total_len} dropped: {cumsum_lens[-1] - total_len} "
-                f"num samples {len(batch)} - rank: {rank} "
-                f"max len: {lens.max()} min len: {lens.min()} avg len: {lens.mean()} "
-                f"num_loss_counted_tokens: {num_loss_counted_tokens}\033[0m"
-            )
-
-            return {
-                "input_ids": input_ids,
-                "labels": labels,
-                "num_loss_counted_tokens": num_loss_counted_tokens,
-            }
-
-    else:
-
-        def pad_collate_fn(batch):
-            lens = np.array([len(item["input_ids"]) for item in batch])
-            max_len = max(lens)
-
-            input_ids = torch.stack(
-                [
-                    F.pad(
-                        item["input_ids"],
-                        (max_len - len(item["input_ids"]), 0),
-                        mode="constant",
-                        value=pad_token_id,
-                    )
-                    for item in batch
-                ]
-            )
-            labels = torch.stack(
-                [
-                    F.pad(
-                        item["labels"],
-                        (max_len - len(item["labels"]), 0),
-                        mode="constant",
-                        value=-100,
-                    )
-                    for item in batch
-                ]
-            )
-            num_loss_counted_tokens = (labels != -100).sum()
-
-            attention_mask = torch.stack(
-                [
-                    F.pad(
-                        item["attention_mask"],
-                        (max_len - len(item["attention_mask"]), 0),
-                        mode="constant",
-                        value=0,
-                    )
-                    for item in batch
-                ]
-            )
-            print(
-                f"\033[96m total tokens: {max_len * len(batch)} num samples: {len(batch)} num padding tokens: {max_len * len(batch) - lens.sum()} - rank: {rank} "
-                f"max len: {max_len} min len: {min(lens)} avg len: {lens.mean()} "
-                f"num_loss_counted_tokens: {num_loss_counted_tokens}\033[0m"
-            )
-
-            return {
-                "input_ids": input_ids,
-                "labels": labels,
-                "num_loss_counted_tokens": num_loss_counted_tokens,
-                "attention_mask": attention_mask,
-            }
-
-    return pad_collate_fn
-
-
 def setup_dataset(
     data_path: str,
     mock: bool = False,