| Message ID | 20250301104356.246031-1-mjguzik@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | fs: predict no error in close() | expand |
On Sat, 01 Mar 2025 11:43:56 +0100, Mateusz Guzik wrote: > 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(): > > [...] Applied to the vfs-6.15.misc branch of the vfs/vfs.git tree. Patches in the vfs-6.15.misc branch should appear in linux-next soon. Please report any outstanding bugs that were missed during review in a new review to the original patch series allowing us to drop it. It's encouraged to provide Acked-bys and Reviewed-bys even though the patch has now been applied. If possible patch trailers will be updated. Note that commit hashes shown below are subject to change due to rebase, trailer updates or similar. If in doubt, please check the listed branch. tree: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git branch: vfs-6.15.misc [1/1] fs: predict no error in close() https://git.kernel.org/vfs/vfs/c/c7f3ef71a2db
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;
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@gmail.com> --- 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(-)