linux-kernel - Re: [PATCH] fs: optimise kiocb_set_rw

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Date:   Sat, 1 Aug 2020 13:42:39 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: optimise kiocb_set_rw_flags()

On 01/08/2020 13:36, Pavel Begunkov wrote:
> Use a local var to collect flags in kiocb_set_rw_flags(). That spares
> some memory writes and allows to replace most of the jumps with MOVEcc.

This one is pretty old, but looks like nobody in fsdevel cares.

Jens, any chance you can pick this up? For instancec, I don't like the
binary it generates for io_uring.

> 
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
> 
> v2: fast exit on flags == 0 (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 8a00ba99284e..b7f1f1b7d691 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3282,22 +3282,28 @@ 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