Actually, just measuring the "call time" does not refrect the reality. Results are mixed. Total relative time for the following cases are as follows:
# Time: 1
def foo1():
pass
# Time: 30
@coroutine
def foo2():
pass
# Time: 200
@coroutine
def foo3():
yield
# Time: 2
async def foo4():
pass
# Time: 500
async def foo5():
await sleep(0)
