Add advenced shared prefix support

Author: sjmonson

src/guidellm/dataset/synthetic.py

@@ -1,6 +1,6 @@
 import json
 import random
-from collections.abc import Iterable, Iterator
+from collections.abc import Iterable, Iterator, Sequence
 from itertools import cycle
 from pathlib import Path
 from typing import Any, Literal, Optional, Union
@@ -25,12 +25,29 @@
 ]
 
 
-class SyntheticDatasetConfig(BaseModel):
+class PrefixBucketConfig(BaseModel):
+    bucket_weight: int = Field(
+        description="Weight of this bucket in the overall distribution.",
+        gt=0,
+        default=100,
+    )
+    prefix_count: int = Field(
+        description="The number of unique prefixs to generate for this bucket.",
+        gt=1,
+        default=1,
+    )
     prefix_tokens: int = Field(
-        description="The number of shared prefix tokens to prepend to each prompt.",
+        description="The number of prefix tokens per-prompt for this bucket.",
         ge=0,
         default=0,
     )
+
+
+class SyntheticDatasetConfig(BaseModel):
+    prefix_buckets: Optional[list[PrefixBucketConfig]] = Field(
+        description="Buckets for the prefix tokens distribution.",
+        default=None,
+    )
     prompt_tokens: int = Field(
         description="The average number of text tokens generated for prompts.",
         gt=0,
@@ -169,17 +186,16 @@ def __iter__(
         )
         # ensure diff distribution from output tokens
         rand = random.Random(self.random_seed + 2)  # noqa: S311
+        shared_prefix_iter = iter(self._create_prefixes(rand))
         unique_prefix_iter = cycle(self.processor.get_vocab().values())
 
-        prefix_index = rand.randint(0, len(self.text_creator.words))
-        prefix_tokens = self._create_prompt(self.config.prefix_tokens, prefix_index)
-
         for _, prompt_tokens, output_tokens in zip(
             range(self.config.samples),
             prompt_tokens_sampler,
             output_tokens_sampler,
         ):
-            start_index = rand.randint(0, len(self.text_creator.words))
+            start_index = self._rand_start_index(rand)
+            prefix_tokens = next(shared_prefix_iter, [])
             prompt_text = self.processor.decode(
                 prefix_tokens
                 + self._create_prompt(
@@ -189,10 +205,40 @@ def __iter__(
             )
             yield {
                 "prompt": prompt_text,
-                "prompt_tokens_count": self.config.prefix_tokens + prompt_tokens,
+                "prompt_tokens_count": len(prefix_tokens) + prompt_tokens,
                 "output_tokens_count": output_tokens,
             }
 
+    def _rand_start_index(self, rand: random.Random) -> int:
+        """Generate a random start index for text generation."""
+        return rand.randint(0, len(self.text_creator.words) - 1)
+
+    def _create_prefixes(self, rand: random.Random) -> Sequence[list[int]]:
+        """Create an iterator for shared prefix tokens."""
+        buckets = self.config.prefix_buckets
+
+        if not buckets:
+            return []
+
+        total_weight = sum(bucket.bucket_weight for bucket in buckets)
+        if total_weight <= 0:
+            raise ValueError("Total weight of prefix buckets must be greater than 0.")
+
+        prompts = []
+        for bucket in buckets:
+            for _ in range(bucket.prefix_count):
+                start_index = self._rand_start_index(rand)
+                prompt_tokens = self._create_prompt(bucket.prefix_tokens, start_index)
+                sample_percent = (
+                    bucket.bucket_weight / bucket.prefix_count / total_weight
+                )
+                sample_count = sample_percent * self.config.samples
+                for _ in range(int(round(sample_count))):
+                    prompts.append(prompt_tokens)
+
+        rand.shuffle(prompts)
+        return prompts
+
     def _create_prompt(
         self, prompt_tokens: int, start_index: int, unique_prefix: Optional[int] = None
     ) -> list[int]: