Vast majority of the time the system call returns 0. Letting the compiler know shortens the routine (119 -> 116) and the fast path. Disasm starting at the call to __fput_sync(): before: <+55>: call 0xffffffff816b0da0 <__fput_sync> <+60>: lea 0x201(%rbx),%eax <+66>: cmp $0x1,%eax <+69>: jbe 0xffffffff816ab707 <__x64_sys_close+103> <+71>: mov %ebx,%edx <+73>: movslq %ebx,%rax <+76>: and $0xfffffffd,%edx <+79>: cmp $0xfffffdfc,%edx <+85>: mov $0xfffffffffffffffc,%rdx <+92>: cmove %rdx,%rax <+96>: pop %rbx <+97>: pop %rbp <+98>: jmp 0xffffffff82242fa0 <__x86_return_thunk> <+103>: mov $0xfffffffffffffffc,%rax <+110>: jmp 0xffffffff816ab700 <__x64_sys_close+96> <+112>: mov $0xfffffffffffffff7,%rax <+119>: jmp 0xffffffff816ab700 <__x64_sys_close+96> after: <+56>: call 0xffffffff816b0da0 <__fput_sync> <+61>: xor %eax,%eax <+63>: test %ebp,%ebp <+65>: jne 0xffffffff816ab6ea <__x64_sys_close+74> <+67>: pop %rbx <+68>: pop %rbp <+69>: jmp 0xffffffff82242fa0 <__x86_return_thunk> # the jmp out <+74>: lea 0x201(%rbp),%edx <+80>: mov $0xfffffffffffffffc,%rax <+87>: cmp $0x1,%edx <+90>: jbe 0xffffffff816ab6e3 <__x64_sys_close+67> <+92>: mov %ebp,%edx <+94>: and $0xfffffffd,%edx <+97>: cmp $0xfffffdfc,%edx <+103>: cmovne %rbp,%rax <+107>: jmp 0xffffffff816ab6e3 <__x64_sys_close+67> <+109>: mov $0xfffffffffffffff7,%rax <+116>: jmp 0xffffffff816ab6e3 <__x64_sys_close+67> Signed-off-by: Mateusz Guzik <mjguzik@xxxxxxxxx> --- I'm looking at whacking some of the overhead the open+close cycle, this is a side nit which popped up. I'm not going to argue about *this* patch. fs/open.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/open.c b/fs/open.c index 3285d146b0e6..a5def5611b2f 100644 --- a/fs/open.c +++ b/fs/open.c @@ -1579,11 +1579,14 @@ SYSCALL_DEFINE1(close, unsigned int, fd) */ __fput_sync(file); + if (likely(retval == 0)) + return 0; + /* can't restart close syscall because file table entry was cleared */ - if (unlikely(retval == -ERESTARTSYS || - retval == -ERESTARTNOINTR || - retval == -ERESTARTNOHAND || - retval == -ERESTART_RESTARTBLOCK)) + if (retval == -ERESTARTSYS || + retval == -ERESTARTNOINTR || + retval == -ERESTARTNOHAND || + retval == -ERESTART_RESTARTBLOCK) retval = -EINTR; return retval; -- 2.43.0
