The Performance and Scalability working group has a 4 pronged approach for Istio's performance characterization, tracking and improvements:
Code level micro-benchmarks
Synthetic end-to-end benchmarks across various scenarios
Realistic complex app end-to-end benchmarks across various settings
Automation to ensure performance doesn't regress
We also aim to provide guidance for sizing and configuration of Istio installation in production and how to ensure scalability.