Comment 5 for bug 1591193

On terminal run sudo perf record -e cycles -ag and then perf report
iov_iter_init /proc/kcore
       │
       │
       │
       │ Disassembly of section load0:
       │
       │ ffffffff813fbae0 <load0>:
       │ push %rbp
       │ mov %gs:0x14204,%rax
       │ cmpq $0xffffffffffffffff,-0x3fe8(%rax)
100,00 │ mov %rsp,%rbp
       │ ↓ je 2f
       │ mov %esi,(%rdi)
       │ mov %rdx,0x18(%rdi)
       │1d: mov %rcx,0x20(%rdi)
       │ movq $0x0,0x8(%rdi)
       │ mov %r8,0x10(%rdi)
       │ pop %rbp
       │ ← retq
       │2f: or $0x2,%esi
       │ mov %rdx,0x18(%rdi)
       │ mov %esi,(%rdi)
       │ ↑ jmp 1d

Under function iov_iter_init loose 100 cycles!