On Thu, Jun 19, 2025 at 08:08:28PM -0400, Stefan Hajnoczi wrote:
> The io_uring_prep_readv2/writev2() man pages recommend using the
> non-vectored read/write operations when possible for performance
> reasons.
>
> I didn't measure a significant difference but it doesn't hurt to have
> this optimization in place.
>
> Suggested-by: Eric Blake <ebl...@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> block/io_uring.c | 29 ++++++++++++++++++++++++-----
> 1 file changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/block/io_uring.c b/block/io_uring.c
> index dd930ee57e..bbefbddcc0 100644
> --- a/block/io_uring.c
> +++ b/block/io_uring.c
> @@ -49,12 +49,24 @@ static void luring_prep_sqe(struct io_uring_sqe *sqe,
> void *opaque)
> #ifdef HAVE_IO_URING_PREP_WRITEV2
> {
> int luring_flags = (flags & BDRV_REQ_FUA) ? RWF_DSYNC : 0;
> - io_uring_prep_writev2(sqe, fd, qiov->iov,
> - qiov->niov, offset, luring_flags);
> + if (luring_flags != 0 || qiov->niov > 1) {
> + io_uring_prep_writev2(sqe, fd, qiov->iov,
> + qiov->niov, offset, luring_flags);
> + } else {
> + /* The man page says non-vectored is faster than vectored */
> + struct iovec *iov = qiov->iov;
> + io_uring_prep_write(sqe, fd, iov->iov_base, iov->iov_len,
> offset);
> + }
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org
