It seems like kestrel part of .net core got some amazing performance improvements contributions from the open.I see the performance of kestrel is much better than any versions of IIS +ISAPI or IIS7 + Asp.net modules/handlers ever produced.May be this is partly to do with how simple the middleware (just a function/method it is ).But the request parsing logic got really well and I see that kestrel could hit 5 Million RPS disucssed on this talk[1]( compared to 50K of old asp.net) . Some crazy optimizations and benchmarks are discussed in that video like static byte arrays,memory pools,custom awaiter,bit manipulations for string comparisons etc

Kestrel will be one of the best when it comes to benchmark

[1] https://vimeo.com/172009499

[edit] added video url