On 1/17/2020 4:32 AM, Pavel Begunkov wrote:
> 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.
Humble ping
>
> Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
> ---
>
> v2: check for 0 flags in advance (Matthew Wilcox)
>
> include/linux/fs.h | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 98e0349adb52..22b46fc8fdfa 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3402,22 +3402,28 @@ 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 (!flags)
> + return 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;
> +
> + ki->ki_flags |= kiocb_flags;
> return 0;
> }
>
>
--
Pavel Begunkov
