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@eicherseiji eicherseiji commented Jul 8, 2025

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Signed-off-by: Seiji Eicher <seiji@anyscale.com>
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Summary of Changes

Hello @eicherseiji, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the benchmarking suite by adding a new synthetic dataset type, PrefixRepetitionRandomDataset. This dataset is specifically designed to simulate workloads with shared prefixes, enabling more accurate performance evaluations for systems optimized for such patterns. The changes include the implementation of the new dataset class and its full integration into the existing benchmark_serving script with configurable parameters.

Highlights

  • New Benchmark Dataset: Introduced PrefixRepetitionRandomDataset in benchmarks/benchmark_dataset.py. This new dataset class generates synthetic prompts where a fixed number of unique prefixes are randomly created, and then a specified number of random suffixes are appended to each prefix to form individual requests. This is useful for benchmarking scenarios that involve repeated prefixes, such as those leveraging KV cache optimizations.
  • Integration into Benchmarking Framework: Integrated the new PrefixRepetitionRandomDataset into benchmarks/benchmark_serving.py. Users can now select this dataset using the --dataset-name prefix_repetition command-line argument.
  • New Command-Line Arguments: Added a new argument group 'repeated prefix dataset options' to benchmark_serving.py. This group includes arguments like --repeated-prefix-prompts-per-prefix, --repeated-prefix-prefix-len, --repeated-prefix-suffix-len, --repeated-prefix-num-prefixes, and --repeated-prefix-output-len, allowing for fine-grained control over the generation parameters of the PrefixRepetitionRandomDataset.
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@mergify mergify bot added the performance Performance-related issues label Jul 8, 2025
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Code Review

This pull request introduces a new PrefixRepetitionRandomDataset for benchmarking scenarios with repeated prefixes. The implementation is mostly correct, but there are a few areas for improvement.

The main issue is that the sample method in the new dataset has a signature that is incompatible with the base class, which I've flagged as a high-severity issue. I've also suggested a refactoring to reduce code duplication within the sample method for better maintainability.

The changes in benchmark_serving.py correctly integrate the new dataset, but the call to the sample method needs to be updated to match the corrected signature.

Overall, the changes are good, and with these fixes, the code will be more robust and maintainable.

Signed-off-by: Seiji Eicher <seiji@anyscale.com>
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yeah let's test this in our benchmarks to ensure effectiveness before we end up merging it in upstream.


class PrefixRepetitionRandomDataset(BenchmarkDataset):
# Default values copied from benchmark_serving.py for the repeated prefix dataset.
DEFAULT_PROMPTS_PER_PREFIX = 200
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The default value of 200 per prefix seems high, but yeah :)

requests.append(
SampleRequest(
prompt=prompt,
prompt_len=prompt_len,
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if you sum them in the str space it may not preserve the same sum of prefix and decode relation in the token space.

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