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!
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https://bugs.launchpad.net/bugs/1591193
Title:
Useless operation on proc registry
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