Fix Tornado perf regression
Fix Tornado perf regression

`gen.coroutine` has more overhead than first believed.

vanloswang/tchannel,hustxiaoc/tchannel,benfleis/tchannel,i/tchannel,sasa233/tchannel,Zirpon/tchannel,chenwenbin928/tchannel,savaki/tchannel,vanloswang/tchannel,hustxiaoc/tchannel,bunnyblue/tchannel,chenwenbin928/tchannel,RyanTech/tchannel,benfleis/tchannel,RyanTech/tchannel,Zirpon/tchannel,sasa233/tchannel,i/tchannel,sasa233/tchannel,bunnyblue/tchannel,chenwenbin928/tchannel,Zirpon/tchannel,i/tchannel,bunnyblue/tchannel,RyanTech/tchannel,savaki/tchannel,vanloswang/tchannel,benfleis/tchannel,hustxiaoc/tchannel,savaki/tchannel