linux-kernel - Re: [PATCH v3 5/7] iov_iter: optimise bvec iov_iter

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Date:   Mon, 11 Jan 2021 10:55:48 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Pavel Begunkov <asml.silence@...il.com>
Cc:     linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Jonathan Corbet <corbet@....net>, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, target-devel@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-doc@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 5/7] iov_iter: optimise bvec iov_iter_advance()

On Sat, Jan 09, 2021 at 04:03:01PM +0000, Pavel Begunkov wrote:
> iov_iter_advance() is heavily used, but implemented through generic
> means. For bvecs there is a specifically crafted function for that, so
> use bvec_iter_advance() instead, it's faster and slimmer.
> 
> Reviewed-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
>  lib/iov_iter.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 7de304269641..9b1c109dc8a9 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1065,6 +1065,21 @@ static void pipe_advance(struct iov_iter *i, size_t size)
>  	pipe_truncate(i);
>  }
>  
> +static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
> +{
> +	struct bvec_iter bi;
> +
> +	bi.bi_size = i->count;
> +	bi.bi_bvec_done = i->iov_offset;
> +	bi.bi_idx = 0;
> +	bvec_iter_advance(i->bvec, &bi, size);
> +
> +	i->bvec += bi.bi_idx;
> +	i->nr_segs -= bi.bi_idx;
> +	i->count = bi.bi_size;
> +	i->iov_offset = bi.bi_bvec_done;
> +}
> +
>  void iov_iter_advance(struct iov_iter *i, size_t size)
>  {
>  	if (unlikely(iov_iter_is_pipe(i))) {
> @@ -1075,6 +1090,10 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
>  		i->count -= size;
>  		return;
>  	}
> +	if (iov_iter_is_bvec(i)) {
> +		iov_iter_bvec_advance(i, size);
> +		return;
> +	}
>  	iterate_and_advance(i, size, v, 0, 0, 0)
>  }
>  EXPORT_SYMBOL(iov_iter_advance);
> -- 
> 2.24.0
> 

Reviewed-by: Ming Lei <ming.lei@...hat.com>

-- 
Ming