linux-kernel - Re: [PATCH V11 13/19] virtio_ring: introduce virtqueue ops

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Message-ID: <20251226143433-mutt-send-email-mst@kernel.org>
Date: Fri, 26 Dec 2025 14:37:07 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: xuanzhuo@...ux.alibaba.com, eperezma@...hat.com,
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V11 13/19] virtio_ring: introduce virtqueue ops

On Thu, Dec 25, 2025 at 12:26:02PM +0800, Jason Wang wrote:
> This patch introduces virtqueue ops which is a set of callbacks
> that will be called for different queue layout or features. This would
> help to avoid branches for split/packed and will ease the future
> implementation like in order.
> 
> Note that in order to eliminate the indirect calls this patch uses
> global array of const ops to allow compiler to avoid indirect
> branches.
> 
> Tested with CONFIG_MITIGATION_RETPOLINE, no performance differences
> were noticed.
> 
> Acked-by: Eugenio Pérez <eperezma@...hat.com>
> Suggested-by: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/virtio/virtio_ring.c | 173 ++++++++++++++++++++++++++---------
>  1 file changed, 130 insertions(+), 43 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index f804c5c6975a..4e905dc7b6cb 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -67,6 +67,12 @@
>  #define LAST_ADD_TIME_INVALID(vq)
>  #endif
>  
> +enum vq_layout {
> +	SPLIT = 0,
> +	PACKED,
> +	VQ_TYPE_MAX,
> +};
> +

VQ_LAYOUT_SPLIT and VQ_LAYOUT_PACKED would be better.

and VQ_LAYOUT_MAX for consistency.



>  struct vring_desc_state_split {
>  	void *data;			/* Data for callback. */
>  
> @@ -159,12 +165,29 @@ struct vring_virtqueue_packed {