Here's profile of http.go https://github.com/traviscline/web_bench/blob/master/http.go:

        287.36%	runtime.mach_semaphore_wait
         80.46%	syscall.Syscall6
          2.30%	runtime.cas
          2.30%	runtime.memmove
          1.15%	MCentral_Free
          1.15%	MHeap_FreeLocked
          1.15%	bytes.*Buffer·WriteString
          1.15%	crypto/sha256.Init·
          1.15%	hash_remove
          1.15%	runtime.MCache_Alloc
          1.15%	runtime.MHeap_LookupMaybe
          1.15%	runtime.breakpoint
          1.15%	runtime.mach_semaphore_signal
          1.15%	runtime.mallocgc
          1.15%	runtime.xadd
          1.15%	syscall.Syscall

It probably shows that the test is measuring goroutines scheduler and how long it takes for Go to do a syscall.