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A few performance improvements

  • Add Int8/Int4/GPTQ/AWQ quantization with 2-4x memory reduction and auto-detection.
  • Add response cache with LRU eviction for 200x speedup on repeated queries.
  • Add infrastructure for KV cache manager and request batching scheduler.

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Summary of Changes

Hello @lukehinds, 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 significantly enhances the performance and memory efficiency of the LLM inference server by integrating quantization techniques and a robust response caching system. It also introduces a more resilient asynchronous model loading process and lays the architectural foundation for advanced features like request batching and KV cache management. These changes aim to provide faster response times, reduce memory footprint, and improve the overall stability and observability of the service.

Highlights

  • Quantization Support: Implemented support for various quantization methods including Int8, Int4, GPTQ, and AWQ, leading to 2-4x memory reduction. The system can auto-detect quantization from model configurations, and CLI arguments are available for explicit control.
  • Response Caching: Introduced a response caching mechanism with LRU eviction, designed to provide up to a 200x speedup on repeated queries by storing and retrieving generated responses based on prompt and generation parameters.
  • Asynchronous Model Loading & State Management: Refactored model loading to occur asynchronously in a background task, allowing the server to start immediately. A new ModelState struct manages the model's loading status and provides controlled access to the model and its associated caches.
  • API Enhancements: Added new API endpoints for health checks (/health, /readiness) and cache statistics (/cache/stats), providing better observability into the server's operational status and cache performance.
  • Infrastructure for Batching & KV Cache: Laid the groundwork for future performance improvements by adding infrastructure for a KV cache manager and a request batching scheduler, though these are not fully integrated for generation in this PR.
  • Modular Provider System: Introduced a ModelProvider trait and a HuggingFace implementation, abstracting model file fetching and weight loading to support different model sources more easily.
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Code Review

This pull request introduces significant performance and architectural improvements. The addition of quantization, response caching, and asynchronous model loading are excellent enhancements. The new ModelProvider and ChatTemplate traits greatly improve the codebase's modularity and extensibility. My review focuses on a few areas for improvement, including resolving a potential panic in a new health check endpoint, improving efficiency in lock handling, and updating documentation to reflect the new architecture. Overall, this is a very strong contribution.

Comment on lines +413 to +415
} else {
vec![]
};

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medium

If model_state.get_model().await returns an error (e.g., due to a poisoned lock), the function silently returns an empty list of models. This could be misleading for clients. It would be better to log the error to aid in debugging.

    } else if let Err(e) = model_lock {
        tracing::error!("Failed to acquire model lock in list_models: {}", e);
        vec![]
    } else {
        vec![]
    };

batches_created,
avg_batch_size,
queue_size: self.queue_size.load(Ordering::Relaxed),
total_wait_ms: 0, // TODO: track this

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medium

This TODO indicates an unimplemented metric. Tracking total_wait_ms is valuable for monitoring scheduler performance. You can implement this by adding an AtomicU64 for total_wait_ms to the BatchScheduler struct, and then updating it in create_batch like this:

let total_wait: u64 = requests.iter().map(|r| r.wait_time().as_millis() as u64).sum();
self.total_wait_ms.fetch_add(total_wait, Ordering::Relaxed);

Finally, you can use this new atomic value here to complete the implementation.

Comment on lines 409 to +413
pub struct Model<M: ModelInitializer> {
tokenizer: Tokenizer,
model: M,
device: Device,
logits_processor: LogitsProcessor,
cache: M::Cache,
dtype: DType,
pub tokenizer: Tokenizer,
pub model: M,
pub device: Device,
pub dtype: DType,

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medium

The fields of the Model struct are public. This breaks encapsulation, allowing external code to modify the internal state of the model directly (e.g., swapping the tokenizer). It would be safer to make these fields private and provide public read-only accessor methods (getters) for the fields that need to be accessed externally.

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2 participants