Motivation

This PR implements logging for the SGL Router using the tracing. The logging system provides structured logs with timestamps, context information, and configurable log levels.

• Structured logging with multiple log levels (TRACE, DEBUG, INFO, WARN, ERROR)
• Simultaneous logging to console and files
• JSON output format option for log analysis tools
• Minimal overhead implementation with non-blocking I/O
  Safe initialization that prevents crashes when initialized multiple times

Modifications

• Uses tracing, tracing-subscriber, tracing-log, and tracing-appender crates
• Updated documentation in README.md
• Added new logging.rs

Performance Benchmark

To ensure the logging implementation has minimal overhead, extensive benchmarking was performed. The benchmark measured the overhead of logging operations with different configurations:

• Created a benchmark that executes the same operation with and without logging enabled
• Measured the time per operation for:
  • No logging
  • Console-only logging
  • File logging (daily rolling files)

Results

Without logging (total): 99ns for 1,000,000 ops
With console logging (total): 395.498µs for 100,000 ops
With file logging (total): 2.018893ms for 100,000 ops

Time per operation without logging: 0.00 ns
Time per operation with console logging: 3.95 ns
Time per operation with file logging: 20.19 ns

• Console logging: Adds only ~4 nanoseconds per log operation
• File logging: Adds ~20 nanoseconds per log operation
• These overheads are negligible for most operations and will not impact the router's performance

Checklist

• Format your code according to the Code Formatting with Pre-Commit.
• Add unit tests as outlined in the Running Unit Tests.
• Update documentation / docstrings / example tutorials as needed, according to Writing Documentation.
• Provide throughput / latency benchmark results and accuracy evaluation results as needed, according to Benchmark and Profiling and Accuracy Results.
• For reviewers: If you haven't made any contributions to this PR and are only assisting with merging the main branch, please remove yourself as a co-author when merging the PR.
• Please feel free to join our Slack channel at https://slack.sglang.ai to discuss your PR.