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Subject[PATCH] fs: optimise kiocb_set_rw_flags()
Date
kiocb_set_rw_flags() generates a poor code with several memory writes
and a lot of jumps. Help compilers to optimise it.

Tested with gcc 9.2 on x64-86, and as a result, it its output now is a
plain code without jumps accumulating in a register before a memory
write.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
include/linux/fs.h | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 98e0349adb52..c3db8c80aed4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3402,22 +3402,27 @@ static inline int iocb_flags(struct file *file)

static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
{
+ int kiocb_flags = 0;
+
if (unlikely(flags & ~RWF_SUPPORTED))
return -EOPNOTSUPP;

if (flags & RWF_NOWAIT) {
if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
return -EOPNOTSUPP;
- ki->ki_flags |= IOCB_NOWAIT;
+ kiocb_flags |= IOCB_NOWAIT;
}
if (flags & RWF_HIPRI)
- ki->ki_flags |= IOCB_HIPRI;
+ kiocb_flags |= IOCB_HIPRI;
if (flags & RWF_DSYNC)
- ki->ki_flags |= IOCB_DSYNC;
+ kiocb_flags |= IOCB_DSYNC;
if (flags & RWF_SYNC)
- ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
+ kiocb_flags |= (IOCB_DSYNC | IOCB_SYNC);
if (flags & RWF_APPEND)
- ki->ki_flags |= IOCB_APPEND;
+ kiocb_flags |= IOCB_APPEND;
+
+ if (kiocb_flags)
+ ki->ki_flags |= kiocb_flags;
return 0;
}

--
2.24.0
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